I understand your point. I think the decision to not offer fp is multi faceted.
First even though you might have an onsite reservation, you might not get a fp because others had longer stays or because the system crashes (totally Disney's fault btw) with everyone login in at 7am, then those onsite guests are left feeling deceived by the fact that they paid more money and still didn't get a fp
Second the majority of people coming to the parks are off site and local guests. They are def. going to benefit from the no fp attraction
Third it is proven that an attraction without fp moves the line faster
Now I understand people not wanting to wait multiple hours, no one wants to do that, but the fact of the matter is that people are doing it right now, look at FOP, still multiple hour wait times everyday after 2 years being open and with a fraction of what the SW fan base is
So Disney, and obviously this is all just guessing in my part, decided to go with the lesser of 2 evils. Either open with fp and have most guests angry at the long wait plus on site guests angry that they couldn't get a fp OR open without fp and have everyone wait the same amount of time