It is a double standard, but however it's hardly that cut and dry.
Post Series B, if the board does not believe the current Founder/CEO can take the company to the next milestones of growth, they will replace them.
Typically engineering teams need to scale sooner, so you you see a more experienced manager be brought in before the CEO is considered for replacing.
The CEO may also has the additional benefit of having the investors and board help him or her in their decisions.