When I shop for a 2" hitch to add to a particular hatchback, I find that some models will take a 2" hitch, while others will only take a 1.25" hitch.
Why is that? Is this, for example, an indication of the strength of the (tail of a) frame? Is it simply a question of demand, in that no one is asking for a 2" hitch, and so no one bothers to manufacture an add-on hitch?
In case it matters, I don't want to tow anything. I'm looking for a 2" hitch because it is necessary for a four-bicycle rack.
I assume you are looking at no-drill hitches available for your model of vehicle, and other similar vehicles.
This means what you are really seeing is that they make no-drill hitches of one size for one vehicle, and another size for another. The only way to know why that is the case is to contact a hitch manufacturer who offers both and see if they can tell you.
While it could have something to do with the capacities or design of the vehicles themselves (EG strength of mount points, manufacturer tow rating, engine size, etc) it could also just be a matter of market forces, it might just not be profitable for the hitch manufacturers to make a 2" hitch for your vehicle. Maybe there isn't much demand for big hitches for your vehicle, maybe the 2" hitch that fits the similar vehicle you are comparing to also happens to fit other vehicles from the same (or even another) manufacturer which have higher towing capacities/more demand. There are many other reasons a company might make aftermarket part X but not Y for a given vehicle, most of which are not technical.
Ultimately you can have hitch of any size custom made for your vehicle, but you still need to stay within whatever your manufacturer specs are for gross vehicle weight, towing capacity etc. Usually there is a section on towing in the user manual and that all applies here.
