Fascists believe in inequality based on race or gender.

(Neo)liberals believe in inequality based on class or wealth.

So they both believe in inequality. A rich man gets better healthcare, better legal help. Better education. Better food as a child. Have more say and hold more power. Social democrats try to ameliorate that a bit but fundamentally still believe rich man should be above others. This is all right wing from a socialists perspective. This shared belief in inequality also explains how easily they can ally themselves with fascists.