I think the fares are the main one. They have a meter that uses set prices and is sealed by TFL. I guess the idea was that people would always know it was a fair fare or (if they ordered a minicab) that they would pay a fixed fare they knew ahead of the journey. I can see this having its root in consumer protection.

I think the minicab folks are annoyed for the same reason - they can't charge the way Uber does, only black cabs can do that. So uber is in a grey area - it's not licensed to charge by meter, but it kinda-sorta does, and it doesn't charge the rates black cabs have to.

IIRC black cabs are prohibited from using GPS as well... but that seems minor and I may be wrong.