"Sending unruly mobs to private residences, like we have seen with the angry crowds in front of the homes of Supreme Court justices, is inappropriate,” DeSantis said in an email to news outlets.
He connected his signing to the current protests in DC, but those weren't the impetus for the bill.
It was motivated by events in Florida in the past year: Protests outside the homes of Senators Rubio and Scott, by Trump supporters wanting the election overturned, and protests outside the home of Board of Education members who supported masking in the schools.
The bill got bipartisan support, approved 76:41 in the House, 28:3 in the Senate.
But it would have been embarrassing for DeSantis to sign it, since the protests were led by his own supporters (proTrump, antimaskers). Conveniently for him, he was able to announce that he signed it after seeing the crowds in front of SC homes, and didn't have to antagonize his base.