It has little to do with 'ROI' and much more with the way hardware gets made.
Touchpad, touch screens and input devices are actually VERY difficult to get all the details right because you're dealing with material properties, differences that show up in manufacturing and even the geometry of the end user (small hands, big hands, wet hands, etc) among other factors.
Apple takes on the responsibility of their internal hardware (SoCs, all embedded boards, materials) AND software (embedded, OS, drivers, etc). They have a culture of caring about details and do a tremendous amount of R&D on these related details, at the design and manufacturing level, before releasing their product.
In contrast, almost all PCs are made by "integrators" (i.e. Dell, HP, Lenovo, etc) who take mostly off-the-shelf or semi-customized components, "integrate them" (I use it in quotes because often, as we know, products will ship with broken ACPI, EFI, broken drivers, etc) and put it out there. The drivers usually come from a hardware vendor who has little incentive to get "details" right, they will be lightly modified and then the OEM will shoehorn that into a semi-customized OS image and the device ships.
Further, traditional vendors like HP or Dell are under pressure to keep churning out "the next" iteration of their HW, so they don't really go back and improve drivers or firmware unless they are forced to.
On the Linux, FreeBSD and open-source side, you have an army of dedicated volunteers who often take highly sub-par or questionable hardware and work (often in the dark, or through reverse engineering) to make things reliable and add polish. The fact that things work "as well as they do" under modern Linux or *BSD is a miracle and mostly the result of individuals who care. There might be a few individuals at an OEM who care, but by and large the culture is not "we should make the most amazing product and provide documentation and support to the open-source community" and more "if they can get it figured out, good for them".
A more practical detail is the fact most touchpad ICs are made by Alps or Synaptics. And these devices include things like 'palm rejection' and other advanced features that haven't been enabled until somewhat recently because the IC vendor might not have shared the details with the people working on the open-source drivers.
You see nearly the same pattern with Android phones, how long before the next phone gets pushed out? Did they really fix the weird bugs that caused the previous phone to overheat, or the celluar link to drop calls unexpectedly? Fix the fact the satellite GPS doesn't work 1 out of 8 times?
Apple isn't perfect by any means, in fact I find the most current versions of macOS to be VERY user hostile but sadly most OEMs superficially copy Apple (i.e. moving to only ONE or TWO USB-C ports on a modern laptop) and miss the key point of making hardware & software actually working well together and openly supporting something other than Windows.