Why does bitcoin use TCP instead of creating a web server and using HTTP to comunicate between the nodes?
What's the advantage of using TCP over a HTTP server?
Is that important?
Http is a protocol that works on TCP. So if you have an http-server, it uses TCP to communicate anyway. The better question would be "Why should they use an http-server if they don't need it?".
They don't need/want to show a website. They just want to send binary information easily and want to be sure that the other peer received it completly/correctly. And TCP is the perfect protocol for that.