We left the SF Bay area and moved to the Sierra foothills in California. Close enough to drive back for work if needed, but where (at the time) housing (and land) was much more affordable.
I only have two acres. I'm not doing anything commercial. Our home was someone else's retirement dream originally - custom built home, basement, small vineyard of a little over 100 vines, fruit trees.
In a good year, we can yield 80-100 bottles of zinfandel, made in a "natural winemaking" style. After years of trying to do too much, my only real goal this year is to get my first chickens going.
To answer the question in the original post, "why aren't..?", I know quite a few reasons, having been doing it myself.
To summarize and expand on what others have already said in other comments -
It is hard to monetize or turn a profit at it. This is 100% true especially when you compare earnings for your software work vs your intensive manual labor. You probably have to being doing it for the love of it and the for love of self sufficiency. If you are thinking about anchoring earnings in a quantitative sense, consider shifting your thinking to all the qualitative aspects instead.
I agree with another comment that much of our industry is probably in a demographic where they don't want to do physically taxing work. Think about how different physical work can tax your body compared to just exercising - if you go to a gym, jog, etc. you can have a routine you specifically design to not overexert yourself. If you order 40 bareroot trees, you're going to have to get them all in the ground within a limited time frame, or lose them. You may be reaching out at odd angles, over-using specific muscles, getting injured, etc. in this type of work.
Also agree that it is not easy! There is significant domain-specific knowledge you will need to commit to learning, in addition to keeping up with the latest tech trends. Probably nearly everyone who has grown any significant number of plants or raised animals has lost plenty. It takes knowledge and experience to get it right. And lots of knowledge is location specific - different parts of the world have different limiting factors, whether it's summer heat, winter cold, short growing season, high winds, predator/pest/disease species. You really do have to find it interesting and put in the time learning. At this point my mind is an encyclopedia of plant knowledge compared to most but I'm still learning about new species every year.
I'll add that, in order to get out, afford some space, etc. you'll likely end up in a rural area. Be fully prepared to get used to going without some of your city comforts. I can't get an Uber driver to pick me up at my house and take me downtown for a night out. Last summer I heard a Bay Area person joking to a friend, "so, been to all two restaurants out here?" Not quite fair, there are some really good places to eat and significantly more than two, but absolutely way fewer options than any large city or suburb. And lots less going on in terms of night life.
It can take some looking to find the right balance of modern amenities and rural charm. We have a modern hospital, a new cancer center, lots of grocery stores, a few small downtown areas, and three or four farmers markets, but a residential population a quarter the size of the suburb of the Bay Area we left spread out over an area significantly greater in size.
To build on this though, offer some good points and illustrate how I wish more of us would do this...
It is incredibly rewarding to see a tree you planted yourself go from palm size to twice your own height.
Local and home production can hedge against supply chain instability. It's a great pastime and/or profession and ideally more of us would be doing it. In an increasingly uncertain world, leveling up in good old-fashioned self-reliance is quite comforting and enjoyable.
Importing your tech worker salary to a region with few employers and less opportunity can make an impact. Tip your servers generously. Shop at local businesses. Hire local contractors and professionals. You might make a big difference. Keep in mind that your tech salary alone could easily be a few times the median household income of the region.
And just... be closer to nature. Observe the cycles of the seasons. Get used to seeing deer every day and accept that they want to eat everything you grow. Enjoy the less frequent sight of hawks and foxes or even a bobcat. Notice how many mushrooms sprout all over after the rains. Go a week, or more, without needing to leave your property. Realize that everything around you is part of nested, hierarchical self-organizing systems. Accept that human beings are a natural part of this world and at our best we can be caretakers of all that is alive.