Because the AGPL left more ambiguous the scenarios where the user would be compelled the open source their work that used the AGPL licensed work: this unfortunately led many people and organizations to rule out the use of a AGPL software. Google and Amazon in particular are known to have these carte blanch rules in place.
While an open source maximalist might be happy with that ambiguity, if it impedes the use of the software and hence the chance that a broader community of open source will thrive, it arguably backfires... SSPL aims to make explicitly clear that it is in context of building a public service for the software that the copy left provisions of an expectation of open sourcing occur.
The theory is that this allows the software to be more widely used and for the community to benefit when a public service open source project is maintained
While an open source maximalist might be happy with that ambiguity, if it impedes the use of the software and hence the chance that a broader community of open source will thrive, it arguably backfires... SSPL aims to make explicitly clear that it is in context of building a public service for the software that the copy left provisions of an expectation of open sourcing occur.
The theory is that this allows the software to be more widely used and for the community to benefit when a public service open source project is maintained