My concern is the likelyhood that companies using MS products will cut corners by using deprecated/unsupported OSs for years after the last security patch, which will lead to security breaches for many consumers.

That likelihood is high, real and current.

They’ve also been killing motorcyclists in Canada, for the same reason.

If they’re smart they won’t do that as they know people are buying their products specifically for that reason.
If they’re smart…

There’s an XKCD for that, although i do think ActivityPub could be improved.