No, they are not called suckers. And that's an unrealistic comparison. Food is one thing, supporting your pro football team is another. It's called loyalty. Some people understand it, some people don't. Even if you DO want to compare to a restaurant serving bad food, there ARE people who are loyal enough to go back time and time again when there are better options.
You're the sucker for actually believing that someone would be a 'sucker' for being supportive for many years.