Earlier quoted context omitted.
Because of the closed extensions situation, the open source part feels insincere. Sort of like a free plan up to 10 users and then pretty expensive situation. The purpose isn't the free plan, it's just an advertising measure to get people to where you really benefit eventually.
I recently called this (and other Microsoft behavior) out as being "fake" open source. The comment was highly controversial with quite a battle of up and down votes - so clearly not everyone agrees. In my opinion, Microsoft wants the good vibes and PR that comes with open source, but they don't actually want to be open source. Its why many people still don't trust them in this arena.
Yes, Microsoft has an history, yet it isn't as if there is any big corporation doing full open source across all their products, the large majority only does the part that somehow brings good vibes, cuts down their own R&D costs, or is a kind of suble way to find out about possible new employees.