I think Sanders would have probably had a higher initial success rate if he'd been pitching a business opportunity to people that make a living from investing in multiple high risk ventures, rather than pitching the opportunity of becoming a franchisee to people whose roadside cafe was doing just fine, thank you very much.
The story, though I know only bits and pieces, is fairly interesting. In particular, Kentucky Fried Chicken (it wasn't delettered to "KFC" until 1991), like McDonald's and Burger King, capitalised hugely on the building of the Interstate Highway System (begun in 1958), and a sudden interest in familiar food whilst on the road, an experience far more Americans began sharing in the 1960s and 1970s.
To that extent, his company and legacy are a very fascinating study of complementary developments and capabilities. And sinking money into the Colonel in the early 1950s would have given extremely strong returns.
Related to this point, I think I read that Sanders previously had an inn (small hotel) located on a local road. The new Interstate Highway bypassed his inn, thus causing his business to tank. So, I guess KFC was his pivot in the face of a new disruptive technology (interstates).
I've run across a few histories. Robert J. Gordon spends quite a bit of time on the 1950s (his own teen years, I believe), and the culture surrounding them. Including fast-food, entertainment, cars, and freeway culture.
There's a pretty good general biography of Sanders floating around somewhere online though I can't seem to find it. A long-read type piece that starts with his gas-station shooting incident.
My point was less about the specifics of the fried chicken restaurant industry and KFC corporate mythology and more about the fact professional investors earn a living trying to pick winning startups; small business owners that decline to become a franchisee or reinvent themselves as a joint venture with you don't. As such, reticence on the part of the latter group to get involved says a lot less about potential weaknesses in your business model than reticence on the part of the investors.
(FWIW There are plenty of investors that specialise in investing in restaurant outlets and consumer brand franchises, they just don't tend to be located on Sand Hill Road.)