Marxism is widely identified as the intellectual underpinning of Communism, but Marx's philosophy has been hugely influential beyond just that particular economic model. For example, Feminism is often said to be rooted in Marxism, so it's arguable that many of those who identify as Feminists are also Marxists-by-proxy.

As is often the case in philosophy, Marx was brilliant in critique, but lacking in his prescription. Philosophy tends to be great at asking questions, but not so much at answering them.

I suspect many intellectuals who call themselves Marxists identify with Marx's critique — which arguably still stands and a brilliant and revolutionary body of thought — but not with some of its eventual realizations.