They inspire people who follow their precepts to angrily fight against some perceived establishment.
They’re all products of the 19th century and are considered heroes in 21st century academia..
It’s true that when people like one, they usually like all three. Sort of, “If you like Darwin, you’ll LOVE Marx. If you like Marx, you’ll LOVE Nietzche. And if you like Nietzche, well, have WE got a treat for YOU!”