NYC just basically differed on upgrading to a modern signalling system.
Its 100 years old and still using the 70+ year old system. It should have been replaced in the 90s and 00s but here we are and only 1 line has it (the L) and one soon will (the 7). Other countries are lucky because 1) they're not 24/7 and have more time to repair, and 2) were built with the new tech and don't need the retrofitting which the politicians are loathe to do instead of their fancy ribbon cutting ceremonies.