Think what you like. Companies are acquired all the time without a public bidding process. The only times it becomes a public thing is when a company announces that it wants to be bought or in the case of a hostile takeover.
I understand you think that Microsoft is a monopoly in the game space. That's wrong but I don't expect you to believe it. And again, there was no 'bidding' as such. People sat down and worked out a deal. No one is legally forced to announce they're in negotiations to be acquired or merged. It's not how it works.