Your source only addresses NFL City's there are many larger TV markets that do not have NFL Teams in the country. Toronto's is the largest untapped market in the NFL. Due to geography the Bills are landlocked for other TV markets East NYC, South Pittsburg and West Cleveland. The reason Toronto and most of the country doesn't support the Bills is largely due to their pathetic performance over the past 14 years. If we win, we will generate more support it's just the way it works. Winning brings prime time games and national audience, which equal more merchandise purchased. Currently the Bills are irrelevant outside western NY.
The other major source is the lack of major corporate sponsors thanks to NY taxes chasing them away. That's another discussion for another day.
Just win baby