Offtopic: as someone from India, I've seen a lot of American farms and farmers on YouTube but I don't see British farmers on YouTube, why is that?
As an aside, I love UK produce and when it's available to me in the US I'm generally quite happy with it. France probably makes the best butter, Le Beurre, but it's too expensive for me to use regularly. British Double Devon is a true delight and even something basic like Kerrygold is very present and better than 90% of commercial US butter. I'm lucky enough to live down the road from a nice dairy farm and get most of my butter from them, but the UK has some truly good butters at an affordable price.
Tom Pemberton: https://www.youtube.com/c/TomPembertonFarmLife
Olly's Farm: https://www.youtube.com/c/Olly’sFarmLtd
The Hoof GP: https://www.youtube.com/c/TheHoofGP (good one)
You're absolutely right in that most of the food we eat in the US is grown on a relatively small number of huge commercial farms, but interestingly enough about 80% of the ~2 million farms in the US are classified as small, which means they earn less than $350k annual revenue. That's 1.8 million small farms in the US, by comparison there are ~200,000 farms total in the UK. It's just a numbers game, there are vastly more farms in the US than the UK.
Keep in mind, many of these small farms are __very__ small, half of them generate less than $10k annual revenue and 80% earn less than $100k. At that scale they can't compete on price, so they usually focus on the quality of what they grow, and for that to work you have to market your crop which means farmers markerts, facebook, youtube and any other way they can think of to get their product out there.
Also at the $10k or less annual revenue level (about 1 million farms), often the the farm is only nominally a business and in practice it's closer to a hobby or lifestyle. I live in a semi-rural area that's close to a high-income metro and there's always been a constant stream of people retiring from city life to go live in the "country" and farm, in most cases they have savings or other income and only sell their produce to offset some of the cost of production or just because they are proud of their produce.
It’s definitely the answer to why do we have so many small to medium farms. If you really really want to do it, anyone (with some money and a shitton of work) can buy land and try to grow things on it - this is not the case in most of the world, population density in places with farmable land tends to be too high to be generally accessible to the bulk of the population.
Not to mention that there are numerous ways to shelter savings from taxes by having a bare-minimum farm.