I was thinking of a different way to phrase the question of how and why people farm...and a way that would work with the data presented by the USDA ERS. As I was drifting off to sleep, it occurred to me that it was pretty easy to operationalize "hobby farms" and "hobby farmers" with the data presented. One of the statistics is farms underneath 10,000 a year in SALES (that is gross, not net. 10K a year gross isn't a lot of money) and another is farmers who, as the saying goes "have kept their day job". The numbers of farms that produce less than a living amount, and the number of people who have to seek their living elsewhere, should more or less add up.
But you have been reading for a while, so lets see what really happens...
The basic view is, as is usually the case, more or less correct, but the trend doesn't jump out at me. Also, many of the states add up to much more than 100, meaning that there are lots of people whose primary income comes from a farm making less than 10K a year gross. I guess that would make these people more subsistence farmers than hobby farmers. At least in some cases; although it is hard to tell from the data presented.
Arizona is especially curious: I at first assumed that it was probably due to some loophole in zoning or tax laws in that state, but I later realized it might have to do with Native American subsistence farmers. Or, the data could have been a typo! Who knows!
It is also interesting to note that in very few states are most farmers primarily farmers, and in most states, most of the farms don't make much money.
"Further research is needed"