...might be due to spread/frequency of different dealerships.
Personally I'm more familiar with Kubota and JD as they're what I'm more familiar with and have seen more of ....where on the other hand I'm not sure I've ever even seen a Kioti tractor in person though there's a dealership a little more than 30 miles away ...and almost every other brand has at least one dealership with a 20 mile radius -- JD actually has three(?), Kubota two (both multi-brand dealerships), and NH, Case, MF, LS, Mahindra, and even RK all have at least one (usually multi-brand) dealership as well.
So really what hasn't been said yet is that the dealer makes the difference. Personally I'm not sure I'd buy a JD in my area just because the nearest JD dealerships are part of a large chain and have (from what I've seen) the stereotypical large chain employee attitudes. Just me, but I'd much rather deal with either the smaller chains or family dealerships that put more emphasis on quality support. For me one of the Kubota dealerships is located on my drive between work and home (makes buying parts/new implements really convenient), is a customer-focused multi-generation family-owned dealership -- which just made it a simple choice since Kubota also manufactures a tractor that had the features/performance I wanted.
Sooner or later everything breaks or needs replacement parts or even just routine maintenance parts and unless it's a disposable item that dealership support or availability of parts is something worth considering. ...especially since not all tractors have the same maintenance intervals. From what I've seen buying oil or hydraulic fluid (and other parts) in the quantities needed for a tractor can also offset initial savings when the tractor is used heavily/routinely.....
No brand loyalty here (last I checked none of them had any to me) - just things I've observed and the things with which I'm most familiar from past interactions.