SSPL is appealing for business but it is not open source. That is a deal breaker for us. We want to remain open source under a license that is recognized as open source.
SSPL is open source by every definition. The OSI rejected it, but their explanation for why boils down to "neener neener" (it's not backed by any facts). Most other organizations haven't bothered to take a position because no notable software uses it and it's not worth the hassle to evaluate (mongodb and redis have better alternatives so nobody cares about them).
late addition: the OSI is a consortium of software and cloud companies; the ones whose business model is ruined by SSPL. They aren't neutral and we probably shouldn't let them be the arbiters of what counts as open source.
Foundations run in a more non-profit, community-oriented way include the FSF, EFF, and Debian, none of which made any significant comment. Debian has excluded SSPL software, but their criteria for inclusion are stricter than simply "is it open source?" and they announced it was simpler to replace them with their superior non-SSPL equivalents than to actually tackle the question.