Maybe because... they don't like it? Lady Gaga sounds like absolute total ****e to my mind, total and utter tedious noisy crap and no scientist is going to tell me otherwise.
If you like pop music that's fine but if you think for a second that it is on par with real music (you know, music that was actually written by the artist, with original lyrics, and instrumentation) then you are simply an idiot.
Also, it's no coincidence that people that stick up for pop on this site almost always write like primary school children. Pop music isn't 'artistic' it is industrial. It has nothing to do with creativity, it has even less to do with individuality (it isn't the consumer that creates the megastars, it's the producers that mold them into something that they already know will be hugely popular). You aren't an idiot for liking it or listening to it, but to pretend that it is about creativity then you are a total and complete moron.
Frankly I wish people would stop lumping pop music in with all other types of music, there is zero to link, say The Beatles, with anything that is currently in the charts. They are not the same thing - they are part of something entirely different.