Something you need to realise about employment is that it's not like university entrance, where if you can get into Oxbridge you can pretty much guarantee being able to get into any lower ranked university you want.
Employers are looking for the person who will be the most useful employee to them. Your university education is not useful to them because the job is just taking peoples' orders, giving them their change, putting pre-packaged stuff into an oven, turning it over and taking it out again. On the other hand, the fact you have a degree means you are more likely to resent working there and try to leave as soon as possible.
In this instance someone who left school after their GCSEs or A levels is actually a better choice. They don't have many other options and are much more likely to stick with the job and work hard at it, and maybe even see being promoted to a junior manager at Pizza Hut as a career they might stick with in the long term.
So don't take it personally.