I don't see how PRG was the busiest route EZY did. It was only done a few times a week. PRG and places like it are low yielding. They don't spend onboard and when Eastern Europe was a la mode for stags and hens there were frequent issues onboard.
Eastern Europe isn't as cheap as it once were. People can drink just as cheap somewhere hotter and safer too.
The portfolio of routes suits the airport and there are many network carriers for those few who do want somewhere a bit more off the beaten track.