I would think it being seasonal would put a big damper on people wanting to do it: if you can only work 6-8 months a year, what are you going to do the rest of the time?
If you're paid enough in that 6-8 months, whatever you want. Plenty of dangerous, limited season jobs exist—but to attract workers they have to pay really well.
How many teachers are there in this country? Safe, seasonal work isn't exactly common but it's certainly not shirked due to not being busy for 3 months. A lot of teachers find that to be a benefit.
If anyone else wants data on this assertion (farming as one of the most dangerous jobs in the US). It certainly appears to be up there, in both gross and per capita numbers. Seems to largely (for agricultural workers) be associated with transportation (not equipment, so perhaps the way many workers travel around fields and all in the back of trucks and similar unsafe methods?).
And the distance from medical care means that severe but survivable injuries become severe and fatal injuries out in farm country. Near my grandparents' farm most of the older folks had moved away precisely because of the lack of access to the (due to age) needed medical facilities. When standard care isn't accessible, emergency and trauma care will almost certainly be worse.