I have always wondered if people make money by patenting, if someone breeds a variety that is mostly used by back yard growers, how many trees of some new variety is really sold? few hundred? I guess if you have them distributed like Home Depot, and you make 5 bucks , then selling thousands might be wel worth it, but that's a lot os "ifs".
Now commercial varieties is a different story, here in the DR, some local dude, brought back Avocado scions from Brazil, of the "Margarida" and got it patented, under another name. "Carla" , which is being planted commercially.
Another Avocado variety, "Maluma" I believe charges 1 dollar per tree royalty. but when you take into account that large plantations plant tens of thousands of trees.
it's might be profitable.
Something that might help with getting patent owners their money, is the fact that import countries are starting to requires that farms in export countries have their trees certified, in other words that , if I have Maluma trees, that all my root stock came from a certified supplier, and the grafting also from certified source. this way products are more uniform. and have better quality control. but this means that every grafted tree that is certified is counted. so there is the possibility of profit. but again as others have mentioned, you need to have a winner, something better than what already is out there. and it takes a lot of money to promote. or you will spend decades. take a look at Kiett mango, its only now in the last decade or so, becoming very popular commercial variety, but how long has it been around?