The parts run by the local government (Transport for London) are cheaper than or required to be the same as the private franchises organised by the national government. The TfL parts are far better, I think that even if they were the same price the vast majority would say TfL do better.

The other places I've been were not qualified of "expensive" because they had dramatic discounts for the privileged ones. e.g. student 18-25 age 10€ - worker 25-65 age 50€ - no work 25-65 free pass if you send a paper to request it.

It certainly surprised me as a tourist- for example Berlin's network is not much less extensive but cost a fraction to use.