There are differences depending on which state you live in. In my state, I need to have my vehicle inspected (to pass air quality tests - DEQ) and re-registered (pay tax and get a sticker) every other year. I don't think people really make it clear what 'going to DMV' means, it probably includes an inspection like this - despite being a distinct location. Yes, every other year I must drive to two locations to complete this process.

Many American families have multiple vehicles. Usually both parents work, and when children are old enough they get a hand-me-down car. So, it's not unusual to have to manage 3+ vehicles. Depending on when registration is 'due' one could visit from 1x to 3x a year.

There are online resources, but to pass the air quality tests you must appear in person. The only way around this in my state is own vehicles which are exempt (pre-1974, and motorcycles), or be in a county which is exempt (most of the land area of the state, but not where most people live). I only know this because my project car is from 1972: I just pay taxes online and they mail me my registration and stickers.

Add into it that DMV visits are common-denominator and tend to be unpleasant (long wait times, confusing processes, having to start over if you mess up... then wait in the line AGAIN) and I think that's why you may see so much talk about it. FWIW, I think there are very few people who enjoy this. It's a past-time, but not one we choose.