Money is their lifeblood. If the donors say you are cut off if you don’t start producing, they have to listen or die, politically.
McConnell probably realizes something these mega donors don't, which is, there's been a fundamental shift among the electorate, who are now wide awake and rejecting anyone who even looks establishment.
We elected Trump because we're sick to death of the cuck Republicans "doing something", namely, serving the interests of their crony capitalist masters and the liberal agenda.
I'm not sure what these people expect McConnell to "do". The game in Washington has changed. Incumbents are now suspects, in the eyes of the voters, and there seems to be little the leadership can (or will) do to change that perception.
The voters want the swamp drained, and are determined to see it done.