I would say a lack of buffer capacity from fewer options for a given thing is huge. I've lived in small cities and currently live in a huge one. In a small city, yes, you might have one of most of your hobbies represented. But maybe there is literally only one Indian restaurant, only one golf course, only one movie theater, only one bar, only one car dealership, only one grocery store, etc. If that one thing sucks, you have literally no alternative. You have to deal with it.

Versus in the city I live in now, there are almost a dozen public courses in a reasonable drive. Dozens of car dealerships. Dozens of hiking trails. Dozens of beaches. Dozens and dozens of everything. I can vet options. I can do the same activity in different settings easily. If I am in one area of town, I have flexibility to find options in that area rather than going with my usual option close to me. I have choice. I have agency. I can take my business elsewhere if I need to, and come out better from it thanks to this huge population being able to support a variety of choices for any niche interest I might have.

And of course in the old days the argument was you could just make do with online shopping. But these days the signal to noise ratio on the internet is so pathetically low, I really value actually holding an object I buy in my hand before I get fleeced buying something online once again. Reviews can't be trusted. Images can't be trusted. I trust my eyes and my hands and if the price is fair, taking it home with me is the best deal on shipping there is. Being in a huge city means there are a lot of brick and mortar businesses. Businesses that probably closed years ago with the death of main streets in smaller cities and towns, but thrive here thanks to a huge population being able to sustain more businesses in a given area, even if many people opt to online shop.