The Airport ones are usually franchised to HMS Host, CAA, etc. and aren't run by SBUX per se. Plus, the airports tend to regulate wireless by using a single provider. LAX is a frustrating place to get internet access, but some of the lounges might have T-Mobile hotspots.

The regular SBUX have Wifi because it's handy and can save you on having internet at home, or just give you an excuse to go work someplace more productive.