I mean, NFL teams have a ton of fans, but there are many teams that don't sell out their stadiums very often if ever. I've never heard anyone ever say that they are a fan of a team because there are so many people in attendance to their games. For example, I went to the Texas game, they had WAY more people in the stands than BYU, but I don't feel any more likely to become a Longhorn fan because of it. It was a neat experience, kinda like going to a luau, neat, but I don't plan on roasting pigs in the sand very often.
Furthermore, I'm not sure of how big a CAUSATION a loud stadium is in regard to team performance. There probably is a correlation, since winning teams have more fans, who attend more games, which makes the stadium louder, but how big of a difference does a loud stadium make? If we put UNLV inside of LES and dressed them up in BYU uniforms, would the team actually win more games than if they played in Sam Boyd stadium?
As for recruits, I would imagine that this might be an issue for some recruits, but again, I wonder how many recruits we would actually lose because there are empty seats in the stadium. My guess is that it would be an extreme edge case.