Sage's version requirement for maxima is almost entirely based on
minor output differences in the doctests. Doctests compare results as
strings, so "2+2" and "4" are considered different, but Maxima often
gets smarter and the former becomes the latter in a new version.
If anyone wants to improve this, it would be really helpful to move as
many of these tests as possible to pytest; or at least, refactor them
to check bool(actual == expected) so that we look only for the result
of "True". We waste a lot of time updating our doctests for every
release, and then users waste a lot of time recompiling the brand-new
maxima that we have to require to pass the new tests.
Anyway, the good news is that if you don't care about 100% strcmp()
doctest compatibility, you can usually edit out the version bound and
the old version of maxima will work just fine.