while there's truth to this, one should consider that actual leftists want a fundamental change in the socioeconomic framework of society. there cannot be a truly leftist society with capitalism as the economic status quo. so they are up against a lot, but it is not impossible. at some point in history, abolishment of monarchy was also a completely niche idea and most people probably thought it couldn't be done.
on the other hand the extreme right not only doesn't want to change the economic model, they are even actively supported by some of the richest and most powerful people on earth because they will defend inequality. and any capitalist, either rightwing or "moderate - liberal" will work against leftist politics because they put the legitimacy of their (sometimes obscene) wealth into question.