Looking at the Swedish railway, the issue is related to budget but the problem is not that simple. The main issue is that the railway system lacks redundancy in track capacity, meaning that any failure require short term fixes in order to reduce short term losses. Those short term fixes eventually leads to overall higher downtime and higher failure rates, which only lead to a even more focus on quick fixes and shoddy repairs. Building out new capacity becomes too expensive and takes too long time, and takes money from the budget that is needed to do all the quick fixes that pop up. When those lines become too popular, the pressure only increases to continue do quick fixes, since any downtime has even larger impact both on the straining cargo traffic and passenger throughput.

It becomes like the meme when people talk about nuclear power. Sure, it would had been an good idea 10-20 years ago, but there is no time to do it now and it cost too much. Next year will be even later, and it will cost even more. Any new funding need to be channeled directly to the starving short-term budget, which will continue to always be too low on funding.

One differente with nuclear power is that today we have a better option - renewables - and so nuclear doesn't make sense at all any price. By contrast we don't have anything completely better than mass transit for some cases and to it makes sense to build it and make it cheaper.