Pizza Express is a known good. It's not the best, but it's guaranteed to be consistent everywhere. It does the job when you just want a "good enough" pizza with little fuss.

In contrast, searching for the best pizza carries a risk of getting something subpar and much worse than even Pizza Express.

It's not much different - Pizza Express isn't anywhere near as posh as it thinks it is, and I'd bet the average spend per customer is lower thanks to the constant Tesco Clubcard deals.