Simple. It's "chavtastic" - I.e. it appeals to the uneducated, the uninspired, the X-Factor generation. Secondly, it paints an ethnic/societal minority in a less than favourable light, appealing to the xenophobic masses who use terms like "P*ki shops" in general conversation and read the Daily Star. Thirdly, it's cringeworthy, almost car-crash TV, appealing to the ghoulish curiosity of the modern invasive, voyeuristic TV viewer.
I'm not sure that is a completely fair comment to make about both the show and its viewers. I watch the show, as do many people I know, and personally I find it to be a fascinating insight into a society that is normally closed off from everyone else yet always seems to be around. It's a well made documentary series, yet is also somewhat comical, and I think that's what people like about it.
While it is highlighting what we consider to be problems with their culture, I recon the show is doing them more favours than painting them in a less than favourable light. Not long back most people would have written them off as petty criminals based on the minority who make the papers and slags based on their appearance with no knowledge of how much the other way they actually are.