I think some of the motivation for switching to other small projects is that these won't start costing serious money until after the next general election. How many are shovel ready ?. The worst thing is that nothing will happen for a while and roughly half the money will no longer be spent on rail.
This is exactly what it is, deferring all expenditure on the basis that anything new will take 10+ years to get through planning & parliament. It's simply austerity by stealth.
I wouldn't however give up hope completely. It's a long shot because Labour are being very non-committal, but that's almost certainly to avoid getting caught in the various political traps Sunak has attempted to create.
However Starmer's entire plan for government is based on growing the economy rapidly, and Rachel Reeves plans to deliver this growth with a kind of 'Bidenomics'. Essentially that involves massive debt funded government sponsored private investment, which acts as a fiscal stimulus to drive GDP, which then increases the tax base to repay the debt - just as the Chinese have been doing for years (albeit they push it way too far and build many things that are questionable)
That needs big shovel ready projects. They will off course need to pick over the bones but HS2 offers many opportunities, even if only in parts, and perhaps with private investment like HS1, which will help control costs because investors with skin in the game will be all over it.
They also intend to make radical changes to the planning system, to make projects much easier/quicker to approve, mainly for things like housing, wind farms and power lines, but presumably railways too.