You don’t have to come up with some crazy new innovation for Mag-Lev, just make the trains reliable, affordable, and near major population centers.
One of the advantages of trains is that there can be train stations convenient to where people go within the city whereas airports are often hell and gone. There are more light rails etc. than there used to be but Manhattan, for example, is terrible for getting into the city from any of the airports. Both Logan in Boston and National in DC are pretty good.
LA is sort of a , sorry, train wreck (or at least very variable) for getting around without a car. SF is better the airport is actually at least as good (via BART) getting into the city as the Amtrak station in Emeryville is.
People use commuter rail in Boston, NYC, etc. too but it's generally less useful (or not useful at all) outside of commuting.
It’s fine for the airport to be a bit out there if there is a good rail line going to it.
Here are a few other commutable routes with maglev
NYC - Philly 92 miles
NYC - DC 225 miles
NYC - Boston 215 miles
NYC - Portland, ME 325 miles
NYC - Pittsburgh 380 miles
NYC - Cleveland 470 miles
Cleveland - Chicago 350 miles
St. Louis - Chicago 320 miles
Houston - Dallas 240 miles
Houston - Austin 170 miles
Dallas - Austin 200 miles
Seattle - Portland 175 miles
Las Vegas - Los Angeles 280 miles
But it would be great if all of those were connected by regular 200mph rails, 300mph maglev would be even better. I don't think there's the appetite for the level of investment either one would take.