Limewire isn't a "site," it's a peer-to-peer sharing program. People can "get away" with sharing child pornography in the same way that they can "get away" with sharing the also usually illegal music and movies most people use it for. There is no central site that hosts or monitors these files, and there is no one yet like the RIAA or MPAA attempting to track down and prosecute any possible violators in the porn department.
