Microsoft has had a desktop monopoly for 20 years. They have 90% desktop market share and people don't complain about that. They destroyed their competition yet people complain because Google has 65% market share on a product that people can leave overnight. I'm not sure why people get bent out of shape over Google.
You don't count being fined billions of dollars over that monopoly, being forced by governments to make changes to Windows to help competitors, and being sued by several state governments and others as people complaining!?
That aside, the department of justice could (if they hadn't already won against Microsoft) bring two suits simultaneously. The need to investigate one company doesn't stop you from investigating the other.