I suspect in part because most are likely to be conservative about it and would rather see something like HS2 which can see rail services continue beyond the extent of the new infrastructure without having to change trains.
Yes, people expect high speed transport systems to act like our existing long distance transport systems, but faster.
Optimisation of a maglev solution likely requires a change in paradigm.
Also isn't there complications with junctions, meaning that most routes to date are simple point to point systems?
Yes, junction pointwork is bulky and relatively slow to change position.
Which, combined with the extreme acceleration, leads towards (in the UK context at least) a strong driver to minimise the number of point moves during the operation of the line.
Which probably drives us to a metro-style single stopping pattern solution, that can be operated with no point moves at all (assuming balloon loops at the end of the line).
Whilst some opposed to HS2 would suggest that they would be better, the benefits are more limited, especially given the main purpose of HS2 is about capacity (the speed is there to ensure that the capacity is actually used and to mean that the trains can be longer without actually needing more rolling stock than is currently required, or at least not much more).
As I've highlighted before, if all the 390's were running around with 12 coaches with around 660 seats (an often cited way of increasing capacity for the WCML) or even an 11 coach 80x with around 825 seats (only 70 of which are first class) they would need more coaches to do the London Manchester run than a 16 coach HS2 train.
11 coaches taking 5 hours to run London, Manchester, London and New ready to run back Manchester again, at 3tph would require 165 coaches.
HS2 would reduce that from 5 hours to 3 hours, so due the same frequency but with 16 coaches per train it would require 144 coaches.
Meglev (assuming the London Manchester journey times is 40 minutes) would reduce the round trip time for the ruling stock to 2:20 (mostly as the turn around times are n't score to be reduced compared to HS2 or even classic trains). To run a 16 coach train would require 112 coaches (however that only really works so well as the service is 3tph.
A maglev can harness its short journey times to carry a lot more passengers in a given space though.
If we assume a simple jump of London-Birmingham-Manchester, we would be talking about journey times on order of 21 minutes Lonton-Birmingham, and about 15 minutes Birmingham-Manchester. Total journey time on order of 38-39 minutes.
21 minutes southbound from London St Pancras on Thameslink gets you to a few minutes south of Blackfriars, 40 minutes basically gets you to East Croydon!
Even northbound from St Pancras gets you to St Albans and Luton respectively.
If we had a 400m class 700 we would be looking at a capacity of nearly 3000 people!
And turnarounds would be much smaller in this mode of operation given that the line would be essentially operating as a tube system, not a conventional railway.
The stopping distance headway, even limited to a comparatively pedestrian 1.3m/s/s of service brake is only about 55 seconds. So 10-12 trains per hour is certainly achievable in practice with plenty of wiggle room to absorb disruption.
Termini station would likely have two platforms on the balloon loop (one main, one reserve), through stations would probably have three or four, holding a platform in reserve for failures of trains etc.
EDIT:
I know we are committed to the extant HS2 project, I am simply using London-Birmingham-Manchester as an example of an intercity axis, other axes exist in the UK and are available etc etc etc.