> New spring library? Have fun applying the same changes to 14 different microservices.
On the flip side, at some point monoliths can get large enough that upgrading libraries or runtimes becomes an incredibly difficult problem. When I was at Amazon a major service was finally getting upgraded from Java 7 to Java 8. Took a cross-functional team 6 months (!) to make it happen due to the massive amounts of existing code. And these are AWS engineers who are much technically stronger than average.
I don't condone the 500 LOC style of true microservices, but people tend to go back to the extreme of "just make everything run in the same process with the same runtime and same dependency chain" as if that doesn't come with its own set of headaches.
(also for what it's worth -- in correctly done SOA, you don't need to upgrade libraries in lockstep. So that Spring upgrade can be done on a per-service basis as needed.)