Just because the spend per rider increased over that time doesn't mean the system is getting what it needs though. A newer system will usually function better than a starved system years later naturally because of deferred maintenance and other aging infrastructure ailments even if the per rider numbers have increased. Comparing it just on the per rider spend assumes that the earlier number is enough.
Though I suppose you would have to look at the state of thr system in the 1980s. NYC may have had more deferred maintenance.
[0] More or less, they've stopped during COVID but it's not a great time to do maintenance.