Having "spun off" Mozilla, they're free of any contractual obligations to pay for the actual development of Mozilla itself.
As such, like anyone else, they can take Mozilla at zero cost, slap on a few bits to it (apparently there's a small community of Netscape diehards who can't live without the AIM and Netscape.com webmail integration), and have a no-brainer product.
They have no need to "market" it (not that AOLTW were doing much better than CBM prior), but it'll keep the ad revenue from drying up on all the portal-cancers they've grown.
(Chances are they also noticed they had some sort of semi-profitable Netscape license still going with some slow-moving institution... And/or that slow-moving institutions still standardized on "Netscape" are captive audiences for the ads and portal sludge.)
