Because it's not an effective use of their time. New farm equipment buyers are running big businesses. Shifting their focus away from the business to repair equipment would be as silly as the CEO of Google personally replacing a failed hard drive on an employee's workstation. There is an industry out there that is already worried about the repairs for you. You, not being in that industry, don't need to be.

Like before, those next in line buying used equipment on smaller farms are more likely to have free time to spend on doing their own repairs and may even enjoy doing it as a hobby, but like before, the are limited to what's available on the used market. If the BTOs aren't buying Kubotas[1], it won't be a used option. This segment of farmers aren't choosing what enters the market initially.

[1] And generally they don't, but the big-time snow pushers seem to really like them, so in reality you do have options even on the used market. It turns out that tractors aren't just for farmers.