Not sure what site you are looking at but xbtfreelancer works for me, but maybe it can detect I already have an account so that is why I can still see register available. Does not make sense to close registrations when there are not enough jobs there!
Upwork is also really tough, and I have paid for that service to see new jobs, same as LinkedIn, you upgrade to Premium and actually it does not get you any extra access.
No mate, I'm looking at the same site - xbtfreelancer.com I didn't register because before they had closed the registration and I thought that until now the lines are still close but if its working for you, let's take that they are open for new registrants again.
As for Upwork, well those are freelancing platforms and they have to that to continue giving good service on both ends, freelancers and clients. Those payment schemes will determine on who are those serious takers.