Part of the reason is likely that farming equipment is bloody expensive. A new combine harvester can cost nearly a million dollars, and there aren't a hell of a lot of used electrical machines on the market yet. Each farm will have several machines that currently run on gas or diesel. How many can the average farmer afford to replace how fast?

Electrifying farm equipment has huge engineering hurdles. They need a massive amount of power, which would mean very large and incredibly expensive battery packs. Those batteries would take either a long time to charge, or high current charging stations.

During seeding or harvest the machines often run for 16+ hours a day, and are literally out in the middle of a field. Where is the super-fast charging station going to go? They can't easily travel all the machinery back to home base every night, and there's no way it makes economical sense for a farm operation to get chargers installed at every field.

These are not necessarily insurmountable problems. There are a number of similarities to trucking, for example, and that's an industry that's starting to see electrification now. But the logistical problems are much harder than trucking. The biggest reason that John Deere etc... aren't making electric tractors right now is that no one would buy one, because no one has any infrastructure in place for it.