Sure there are sports and parks anywhere but the volume of museums and galleries, the vast range and diversity of theatre, ballet, opera, music, restaurants, lectures, courses, the multiculture, the metropolis, the history: there is nothing remotely like it. The only city that comes close is Edinburgh.
And it’s quite possible to visit London and enjoy all of those things for a day out or weekend.
8 million Londoners are not all going to the ballet once a month/a year or even at all. I would guess that most are spending free time doing the same things people do everywhere - dog walking, seeing friends, children’s sports, gardening, watching and participating in sport.
Many Londoners travel to the coast and countryside every weekend.
You just decide what you want to do and adapt your life accordingly.