If instead you would accept that you can wait up to five minutes, and "other people" are nice enough and so you can share a space with them - we could have a nice transit system.
The five minute time I used above is not arbitrary. While there is some debate on the exact number, 5 minutes allows for a lot operational things that are really nice.
There's no logistical reason, but very few municipalities have the density to support that kind of frequency (via fare revenue), and taxpayers (especially in the US, but in other places as well) don't want to pay for all that unoccupied space on trains and buses.
I'm not saying that's a universal truth. There are a few places that do have the density to support that. And there are a few places that don't, but local residents are happy to pay more in taxes to get that kind of frequency. But most places are not like either of those things.
Note that by good transit system I mean one where you never check the schedule because the next bus/train is never more than 5 minutes (that is a maximum time). By good transit I also mean a system of transfers to express service so you can get to more distance places quickly. Nobody in the US has a good system (NYC's subways don't even come that often!), but there is no reason we can't have that, and some places in the world do have it (at least for a few).