Yeah but it was more like “Kanye West paying someone to paint his crib” than “‘middle-class couple hiring a local guy to do up their flat”. Rich people were few and far between.

Fine art was available to more of the population than you'd think. The world population doubled in the past 45 years. In contrast, during the Roman period, the world population took about 500 years to double.

Wealth accumulated over generations. In that time, if your great-great-great grandfather had a piece of artwork, there was a good chance it was yours now.

We have negative stereotypes of the past, and there were periods of history when that was true, but there were advanced periods too. The Bronze Age empires were pretty impressive until roughly 1300 BC. We had a dark age for a while. The Roman Empire was very impressive. Then we had a dark age for a while.

And you also want to think of the social structure. Rich people employed poor people in households. Even if I owned nothing personally, I'd be exposed to art in my master's household.

Except something like 98% of the population were farmers and most of them were never allowed into a rich man’s house

More like 70% to 90%, just the city of Rome got up to 750k-1M people let alone all the other cities in the empire. A great deal of this was due to Egyptian farmers ability to grow multiple crops per year on the same land. Fishing was similarly extremely productive in terms of labor to food production.

I remember reading somewhere that urbanization in Roman Empire was higher than before and after. Like 20% or something.

This is not really true. The rich (patricians) formed entire houses and used combination of wealth and political influence to maintain their positions. Even if their number wasnt greater than few thousands, they de-facto owned the Italy during Roman Republic.

Relatively speaking, they were most numerous within Rome, but they also owned lands they had lower class people and slaves farm for them that they sometimes visited.

You are describing art being commercialized, but not commoditized; a one-off commission based artwork is not a commodity.

I can look online now and see beautiful art whenever I want. In magazines and books beautiful imagery is ubiquitous.

Art is just a thing we expect to see now and is easily reproduced. We are surrounded by it. This is why I chose "commoditized".