I can explain it to you, but I can't make you understand. Greater number equals more votes, but more importantly more people to contribute financially translates to more money.
But to address your point directly, do you think it makes sense to only recruit billionaires? To me that sounds like complete idiocy. Rinella would love it - all the money and none of the crowding, but it is entirely unrealistic.
Here is a quote from an article on the NRA's influence which may help paint the picture.
"Sheila Krumholz, of the Center for Responsive Politics, said it's not just money that gives the NRA influence, but its membership of nearly five million activists.
"The money is a megaphone for another significant asset: a powerful base," she said."
The powerful gun lobbying group spent a record amount on politics last year, and it's paying off.
www.usatoday.com