Sad fact is, there isn't the ridership to support a SkyTrain metro system. Also, Gerald Fox, a noted American transit expert shredded the so-called Evergreen line business case. The following is an excerpt from Fox's letter.

The Evergreen Line Report made me curious as to how TransLink could justify continuing to expand SkyTrain, when the rest
of the world is building LRT. So I went back and read the alleged "Business Case" (BC) report in a little more detail.
I found several instances where the analysis had made assumptions that were inaccurate, or had been manipulated to make
the case for SkyTrain. If the underlying assumptions are inaccurate, the conclusions may be so too.

Specifically:

Capacity. A combination of train size and headway. For
instance, TriMet's new "Type 4" Low floor LRVs, arriving later
this year, have a rated capacity of 232 per car, or 464 for a 2-
car train. (Of course one must also be sure to use the same
standee density when comparing car capacity. I don't know if
that was done here). In Portland we operate a frequency of 3
minutes downtown in the peak hour, giving a one way peak
hour capacity of 9,280. By next year we will have two routes
through downtown, which will eventually load both ways,
giving a theoretical peak hour rail capacity of 37,000 into or
out of downtown. Of course we also run a lot of buses.
The new Seattle LRT system which opens next year, is
designed for 4-car trains, and thus have a peak hour capacity
of 18,560. (but doesn't need this yet, and so shares the
tunnel with buses). The Business Case analysis assumes a
capacity of 4,080 for LRT, on the Evergreen Line which it
states is not enough, and compares it to SkyTrain capacity of
10400.!

Speed.

The analysis states the maximum LRT speed is 60
kph. (which would be correct for the street sections) But
most LRVs are actually designed for 90 kph. On the
Evergreen Line, LRT could operate at up to 90 where
conditions permit, such as in the tunnels, and on protected
ROW. Most LRT systems pre-empt most intersections, and
so experience little delay at grade crossings. (Our policy is
that the trains stop only at stations, and seldom
experience traffic delays. It seems to work fine, and has little
effect on traffic.) There is another element of speed, which is
station access time. At-grade stations have less access time.
This was overlooked in the analysis.
Also, on the NW alignment, the SkyTrain proposal uses a
different, faster, less-costly alignment to LRT proposal. And
has 8 rather than 12 stations. If LRT was compared on the
alignment now proposed for SkyTrain, it would go faster, and
cost less than the Business Case report states !

Cost.

Here again, there seems to be some hidden biases.
As mentioned above, on the NW Corridor, LRT is costed on a
different alignment, with more stations. The cost difference
between LRT and SkyTrain presented in the Business Case
report is therefore misleading. If they were compared on
identical alignments, with the same number of stations, and
designed to optimize each mode, the cost advantage of LRT
would be far greater. I also suspect that the basic LRT
design has been rendered more costly by requirements for
tunnels and general design that would not be found on more
cost-sensitive LRT projects
Then there are the car costs. Last time I looked, the cost
per unit of capacity was far higher for SkyTrain. Also,it takes
about 2 SkyTrain cars to match the capacity of one LRV. And
the grade-separated SkyTrain stations are far most costly
and complex than LRT stations. Comparing 8 SkyTrain
stations with 12 LRT stations also helps blur the distinction.
Ridership. Is a function of many factors.

The Business Case report would have you believe that type of rail mode
alone, makes a difference (It does in the bus vs rail
comparison, according to the latest US federal guidelines).
But, on the Evergreen Line, I doubt it. What makes a
difference is speed, frequency (but not so much when
headways get to 5 minutes), station spacing and amenity etc.
Since the speed, frequency and capacity assumptions used
in the Business Case are clearly inaccurate, the ridership
estimates cannot be correct either. There would be some
advantage if SkyTrain could avoid a transfer. If the
connecting system has capacity for the extra trains. But the
case is way overstated.
And nowhere is it addressed whether the Evergreen Line,
at the extremity of the system, has the demand for so much
capacity and, if it does, what that would mean on the rest of
the system if feeds into?
Innuedos about safety, and traffic impacts, seem to be a big
issue for SkyTrain proponents, but are solved by the
numerous systems that operate new LRT systems (i.e., they
can't be as bad as the SkyTrain folk would like you to
believe).
I've no desire to get drawn into the Vancouver transit wars,
and, anyway, most of the rest of the world has moved on. To
be fair, there are clear advantages in keeping with one kind
of rail technology, and in through-routing service at
Lougheed. But, eventually, Vancouver will need to adopt
lower-cost LRT in its lesser corridors, or else limit the extent
of its rail system. And that seems to make some TransLink
people very nervous.
It is interesting how TransLink has used this cunning
method of manipulating analysis to justify SkyTrain in corridor
after corridor, and has thus succeeded in keeping its
proprietary rail system expanding. In the US, all new transit
projects that seek federal support are now subjected to
scrutiny by a panel of transit peers, selected and monitored
by the federal government, to ensure that projects are
analysed honestly, and the taxpayers' interests are protected.
No SkyTrain project has ever passed this scrutiny in the US.

TransLink's Evergreen Line business case - no better than a Bre-X share!