Slap "Sanctuary City" Leaders with RICO

The Racketeer Influenced and Corrupt Organizations Act (RICO) provides substantial federal penalties for crimes committed as part of an ongoing criminal enterprise. Penalties can include 20 years in prison and/or fines of $25,000.

If a person or group commits any two of 35 crimes in a ten-year period with similar purpose or results, the provisions of RICO may be applied. The applicable crimes and threats include murder, bribery, theft, money laundering, fraud, robbery and dealing in controlled substance. Also included under RICO are violations of immigration law related to bringing in and harboring aliens for purpose of financial gain.

Given all that, would someone chime in and tell me why "sanctuary city" leaders are not prosecuted under RICO for harboring illegal aliens? And why are business owners not prosecuted under RICO when they facilitate the transport, housing and employment of illegal aliens?

It appears that many specific cases of ongoing criminal conspiracies could be developed where the alien smugglers (coyotes) worked in unison with alien harborers (sanctuary city leaders and business owners and, recently, churches) to violate a smorgasbord of laws. As I understand, the conspiracy can still be proven even when the key individuals don't, in fact, actually know each other.

So, the question sits. Can RICO be used against prominent immigration law scofflaws? And, if it can, why isn't it?