Based upon Kromm and SJ's statements, GURPS is a net breakeven, or even a slight loss. Only a handful of sublines make a profit: Transhuman Space, Dungeon Fantasy, and several licensees - but much of that profit is for the licensees, especially since SJ has fairly strict editorial standards for its GURPS licensees. The cash cow was GURPS: Traveller... it subsidized the rest of GURPS except THS.... and DF was the next (and current) cash cow, with THS still supporting itself.
SJ, however, has noted his current creative agenda is on The Fantasy Trip, not GURPS. TFT does have a licensing program. It requires using Warehouse 23, rather than DriveThru, but it's very much modeled on the Wizards/Mongoose/Free League limited licenses. (DM's Guild, TAS, Free League Workshop, respectively.)
SJ is active in the TFT subforum on sjgames, in a way he's not been in most of the board's subforums. TFT is his baby, and he wants to see it flourish. It's simpler than GURPS, and much more suitable for 3rd party additions than GURPS... And was the game that secured his place in the Game Designers Hall of Fame. I expect GURPS is on permanent life support - the costs of keeping it available are low, but the costs of new materials are not.
Note also: SJ himself is directly the designer for OGRE, GEV, Illuminatis, Melee, Wizard, and In the Labyrinth, as well as a dozen other microgames. ITL, the module which turned Melee and Wizard into a full up RPG, was proof he was multi-talented. He's also said to be active in the conceptual and editorial directions of SJG, despite having handed off the reins for day to day operations. OGRE/GEV has had consistent sales since 1977... and several revisions since the original cardboard box. TFT has had calls for reprints since SJ left Metagaming. He couldn't afford to buy it, and it still held a stupidly high relaunch kickstarter once SJ used the Copyright Recovery Act for its intended purpose - returning rights to a unused intellectual property to its creator, even tho' it was sold to or was work for hire from the non-using owner.
TFT is one of the games I keep a copy of (in the non-SJ version, Dragons of Underearth) in my "instant RPG game" box in the car. Right next to GW's Judge Dredd, and the KAMB SDE and SGtC...