This thread has covered a lot of ground now, but the demographic point is important.
In the 2000's, tabletop RPGs fell off a cliff. Aside from D&D, which endures as ever. But it's worth noting that Traveller was a non-starter in that era, pretty much. GDW was long dead, SJG carried the flame for a while, then a bit later Mongoose came along.
Then... a strange thing happened. Kids started watching each other play games, and one of things was D&D. NOT "tabletop RPGs" to any great degree, just D&D. My 25 year old daughter barely plays any tabletop, but she's enough of a Critical Role fan that she travelled interstate to see them live. And bought merch.
So we pretty much have a division between the older gamers who played the games back in the day, and the younger ones who are quite focussed on online and streaming, with the tabletop experience a quaint variation. VTTs and players being physically located all over the globe are the norm now. And when they meet face to face, it's still D&D.
But if you look at the genres played, there's another big strike against Traveller. Space fiction is a ghetto. The most popular non-medieval fantasy genre is horror. The most played space game may be Starfinder, which is obviously an easy switch for the Pathfinder and D&D kids to try out (and is in fact a well thought out space opera, not just a reskinned Pathfinder). Cyberpunk usually does well on the play charts, which is not hurt by the video game.
Traveller is left to pick up the crumbs amongst the indies and the other legacy games played by old people.