What do you propose the devs do though? Take the repo down? I've seen plenty of others who enjoy a deprecated software so they fork it an maintain it.
A good example. Look a the official Argon2 reference implementation. Yeah the same Argon2 that powers a large number if not the majority of password hashing all over the place. It hasn't been maintained in 4 years. No one has touched in in C or libraries that port it. There are some alternatives but none that match the reference in terms of completeness and performance. I assume other languages have attempted to maintain it, but there are 0. I mean literally 0 (I checked last week) active forks of the official Argon2 library.