Dealer proximity and local parts availability play a pretty big role.

Both of those things are worth zero when Deere can't supply enough technicians in the planting and harvest seasons to keep those tractors running.

Also an established line of credit basically with the farm makes buying them easier than competitive offerings by other manufacturers. There’s still enormous cultural inertia with Deere.

"I dont understand why people keep buying JD tractors."

Let's get closer to home: why do people buy Windows and Apples, despite a fair few free (really free) alternatives?

Tractors are more plug-replaceable than operating systems. There are only so many ways to eg turn over soil.

Not if you already bought into dongle ecosystem.

I read somewhere recently that the market for old, used JD's has grown dramatically in the recent past.

Is it a case of lock-in with accessories?