Because the insurance company or bank needs t0 make more money off you. That GAP insurance was pushed super hard by the bank I refinanced my pickup with. Like literally I go in to make a deposit and the teller asks me if I want to add it - months later still... I politely decline. (Lease is different and not all leases include GAP - Toyota Finance Leases are a good example of that...)
State Farm for those of us that have it, doesn't offer it in Florida or Alaska (the two states I've had their insurance) but it is automatically included in your auto loan if you did one through them. Not sure that US Bank which bought out SF Bank is doing this. (I doubt it though)