Heavy machinery needed to install them probable not so good for farmland. Also, the best time to build them is also the best time to be growing crops typically. Not to mention, it’s not like they just sit there all by themselves. You have to run cables and such to connect them to the grid. Which would further disrupt the farmland. Then you have to think, you have farmland with irrigation lines, and you are gonna also have high voltage power generation going on. So either in ground cables where you really don’t want them,or above ground cables with towers, further disrupting the farmland. Then add to that things like maintenance and whatnot. Basically a bunch of stuff getting in the way of growing crops when growing crops typically like to be left alone to grow.

At least, that’s what I could imagine off the top of my head. lol.