… sort of. Last I checked, the Make features required by POSIX were very anemic. What winds up all over the Web in tutorials etc. is mainly GNU Make, which is extended way beyond that, including in ways which can become practical necessities pretty fast.

Which would be why my projects use the “GNUmakefile” file name explicitly, even though e.g. I tend to write to POSIX sh where I can rather than following the “bash scripting” trend. I also remember seeing a project in the wild that had a separate GNUmakefile and BSDmakefile, presumably for similar reasons.

If you use only POSIX make syntax, great for you, but there's definitely a barrier compared to what a lot of people are used to thinking of as Make nowadays.

(This is also ignoring the part where “higher probability” at a glance refers more to popularity than to standards compliance, and I don't read the parent as implying being in an environment where POSIX/SUS compliance is directly related to the set of target systems.)