UK Labour has been a "centrist, pro-capital party" for probably your entire life (or at least most of it.) The only reason Corbyn even ended up in front is that a bunch of centrists nominated him as a joke candidate, and they hadn't been paying attention when Ed Miliband had changed the voting rules and accidentally made Labour a democratic party. Of course the membership voted for Corbyn, everybody else was garbage.
Same reason why Trump won the Republican primary in the US - the Tea Party had forced the voting process to be democratic. Unlike the Democratic party, which doesn't even have a vaguely democratic process, culminating in them having absolutely no process in the last election. I still insist that if Sanders had run as a Republican in 2016, he would have been president.