http://www.lasvegassun.com/news/2011/feb/22/reid-vs-brothel-industry/

This can be seen from the article itself. Regardless of what Sen. Reid states, the point is that rural counties are the ones in control and they are the only ones taxing the brothels directly through what are essentially license fees. Those fees are in the tens and sometimes hundreds of thousands of dollars (if Hof is to be believed about the latter in other sources). Not easy for 'rural' (read: poorer) counties to give up at all.