[bobthepanda]

It's important to note historical context.

The New York subway system was built in spurts up to about the 1950s. This means that large sections of it, tens of miles long, become due for renewal at the same time. Contrast this to MTR, which opened short segments in several phases.

There was also a period stretching probably from 1930-1980 where maintenance on New York's subway was completely deferred. No maintenance or replacement was done for the signals at all. So a lot of what has been happening up until now is not only meant to replace stuff that is due for replacement, but stuff that has been overdue for replacement for decades. It takes a lot of time on a 24/7 railway's schedule to fix such a large backlog. And they usually only refresh the backlog with stuff that is both compatible with the entire existing fleet, which is thousands and thousands of train cars.

Coincidentally, since MTR was first developed in the '70s, those signals are due for replacement right about now. From what I have heard MTR is starting to have a much higher rate of failure than previously, which would make sense if the signals are getting old.