At the moment, the voting-age American public seems to be split into pretty even thirds, with one third being slavering fascists, one third being generally opposed to the first third, and a final third who are either totally apathetic or steadfastly refuse to acknowledge any difference between the other two thirds.
McCarthy needed Dem votes to maintain a hold on the speakership, but the concessions he would have needed to make in order to get them would have meant making himself incredibly vulnerable to a career-ending primary challenge. The political incentives don’t line up.