I think the problem with M$ and especially Apple is that since their OSes are very popular their default Apps have a high install base. But since few people actually use them they don’t have the corresponding monthly active users. iMessage for example only serves as the SMS client for most people to receive stuff like shipping notifications or OTPs. I don’t think that will be enough to get them out of being designated Gatekeepers but it explains why their services are not yet decided on.