Because they are ignorant to the facts?
Not arguing, but out of genuine curiosity what are the actual facts around this? I've looked and you instantly fall into a rabbit hole and it's hard to decipher what's actually going on
(1) who or what is paying to keep it running? If it is the "tax payer" then is it city, state, federal?
(2) who or what owns it and has the right to do it with as they please?
(3) how much hard cash is the airport contributing to said owner and/or taxpayer?
(4) is there a critical service this airport provides? Medical, transportation, etc? The LA basin has a very large number of airports in or near it..
(5) who's actually behind pushing to close it? Something nefarious like a private land developer with ties to elected officials or more benign such as a genuine fiscal concern from a private owner who's not making any money, or worse, losing money?
(6) who will benefit the most from it being closed?
(7) who will benefit the most from keeping it open?
I love flying into SMO, and the Uber ride to the pier for dinner or the museums is great fun. The default answer from any pilot should always be "no" to the question "should we close this airport" .. but if there's a ton of high value land there and this airport mainly sees light piston GA going in and out I can sort of understand the question of, are we pragmatically using this land as best as we could?