They get used in burst cycles -- like 10 days straight at harvest time, other times not started for months. Battery cost per kwh used is very low amortized over its full lifespan, but if you only use it to 1% of its capability your costs are now 100x higher.

Now, hang a high voltage wire down from a big-ass catenary, so you don't need batteries, and it'll be cheaper upfront and in use, but nobody does that because of 1. safety 2. if everybody did it the grid would need upgrades

October to April in Saskatchewan.

Almost certainly it's energy density for long running, high load usage.

If a family car energy usage is 1x, then a light duty truck is about 1.5x, and a heavy duty truck doing hauling or towing is about 4x. A medium sized farm tractor would probably be 20x or more.

In that light, it's not hard to see how cars and light trucks could fare well with today's battery energy density, while heavy duty trucks are at the limits. For a tractor, it's not even close.

I do think we'll see smaller tractors going electric in about 10-15 years.