Of all the FAAMG out there, Microsoft arguably has the most diverse revenue streams, I don't see what's surprising with them going after another market (let alone payments). It's just another layer for monetization and doesn't prevent them pursuing their other business lines (it's arguably different teams anyway). Nothing's ever worth it if you take the approach of "It's already worth/earning 100x, adding 1x isn't worth the effort".

P.s.: I don't mean to defend BNPL, IMO it is shark loaning disguised behind late fees. I forgot the exact number but when I did the (ballpark) math for Afterpay you were capping at like 30% in late fees within 3/4 months.