Why do freelancing platforms charge their users?

[Btaliat]

I don't know if you notice but almost all freelancing platforms do charge their users. There are different fees that can be charged by the freelancing platforms. These money charged are used mostly by the platforms to run their platforms and other reasons. Hardly you will see the ones that don't really charge. Do you know any reason why some of them always charge that fees? You can share some of the reasons that you know below.