The reason behind this is the Catholic Church in the US LITERALLY pulls in BILLIONS each year from contracts with cities,states,and the US government itself to provide services to immigrants.
20 years or so ago when Willie Brown was the mayor of San Francisco,he had a city ordinance passed denying contracts to ANY organization that discriminated against homosexuals by not paying unmarried and homosexual couples "spousal benefits" like health insurance. The local arch-diocese filed suit to make the Catholic Church exempt from this ordinance because it conflicted with their religious beliefs.
The court ruled that since the Catholic Church had a right to NOT bid on or hold city contracts and since no one was making them bid or accept city contracts against their will,this was not discriminatory.
So,they had a choice. They could start paying same sex couples the same benefits they had to pay traditional married couples (this was before same-sex marriage was recognized),or they could lose OVER 5 MILLION DOLLARS A YEAR IN CITY CONTRACTS to provide the VERY same services they were already supposed to be providing to justify their tax-free status.
Guess what? The San Francisco Arch-Diocese decided that same sex couples wasn't that big a deal and did NOT conflict with their deeply-held religious view-points at all,and they started paying it.
This was just ONE Arch-Diocese in ONE city,and it was pulling in more than 5 MILLION dollars a year to help the po,the needy,and the immigrants. It doesn't even count the money they pulled in from the people they helped in the form of tithes.
It doesn't even count they state and federal money they pulled in. The 5 million was JUST from the city of San Francisco.
Now,imagine how much they are pulling in 20 years later when there are many millions more Catholic 3rd Worlders here illegally that are being helped by the Catholic Church and sanctuary cities.