1. New construction must meet ADA requirements. 2. Old construction can remain. 3. Repairing broken old construction requires meeting ADA requirements.
So between 2 and 3 you end up with broken old construction that cannot be repaired to "what it was" because repairs must meet ADA requirements.
Each step makes sense on its own, but combined they result in something worse (in particular) even though overall it works out better.
If the new local maximum is "well, we won't fix it at all then" - the usual building code solution is property maintenance codes that mandate repairs.
Then a popular crosswalk gets upgraded before a rural crosswalk that nobody uses anyway. An easy upgrade is done before a hard upgrade. Sometimes even new stuff might be built non-compliant if, for example, there are other substantial benefits that outweigh the fine.
Just burn the fine revenue. (Burning money is the inverse of printing money, helps reduce inflation, and means nobody has an incentive to maximize fines)
They're the ones who can print them anyway. The end result is they just print less each year.
But ADA stuff is almost always handled on a local, not even state, level.
Or, just have a fixed window to achieve compliance or the building is condemned.