Nobody makes the perfect tractor, every tractor will break down and at some point you will need to get parts.
Today's world is a little different than it was 50 or 60 years ago when all you had to rely on was the dealer for parts, now you can get parts by clicking a mouse and they show up to your front door.
I just ordered blades for my Husqvarna mower off Amazon, 3 blades for a 54in deck was $32 including shipping.
I think a lot of it has to do with advertising and a strong following of both Kubota and JD, every time you see a green and yellow monster tractor in a field or 15 of your neighbors driving orange tractors it catches your eye. Case is another with there red tractors.
If I was a farmer, I would pay more for a tractor that I could get parts for in a pinch, peak of harvest and your main tractor goes down, you just can't wait 2 or 3 days for parts, you drive to the dealer and overnight parts if they don't have them in stock, the more readily available parts are the more attractive that brand is I think.
Unless it's a known lemon tractor, resell won't vary that much, my tractor is 12 years old and I bought it for just over 50% it was new, it depreciated almost $1300 per year and racked up 830 hours in that time, that's a lot of money lost but a lot of work done, that's where your gonna recoup your loss, doing it yourself vs contracting out.
Do I think JD, CNH or Kubota works harder than Mahindra and Kioti? No I don't believe so but your paying a lot more for the JD, CNH and Kubota products.
If you really compare apples to apples on the base lines the JD (E series) and Kubota (non grand), the name gives those lines much more value then the capabilities of the tractor compared to Mahindra for example. More bang for your buck if you will.
you shouldn't shop brands, narrow down your range of tractors and pick one or two models from each company and sit and walk around them all, that's what I did and found that I could do more work with the Mahindra 1533 for less money, but ended up buying a used JD instead lol.
A tractor is a tractor, pick the one that excites you the most, the one you will be eager to maintain and no matter which one you pick, it should last a long time.
One thing I will say is, I have a 1950 Case SC sitting in my barn that I can still get parts for in the local case dealer. CNH, JD and Kubota aren't going anywhere anytime soon I don't think, but look at GM and Pontiac, I guess you never know.