Man, how many times are we going to hash this one out?
Since solid state amps became more capable in the early 80s, people have been scratching their chins over the demise of tube bass heads. There is a shift in the market right now, but what else is new.
Here are some things that are getting ignored in the broader conversation.
1.) When the first dedicated bass heads were built, they were slightly tweaked guitar heads. Many early players just used guitar gear. We've evolved a lot since then and come to understand the dynamics of audio more. Guitarists seem to be stuck in the 70s and still love their heavy @$$ cabs and tube heads. Good for them. I don't. I'm not fixated on the 70s and prefer convenience over mystique.
2.) A tube head is great in the studio, and great if someone else is moving it, but sucks something awful when you're gigging around on your own time and on your own dime. Older solid state heads are pretty heavy too, but for the player on the go, can you really beat 500 watts slung over your shoulder?
3.) The internet has changed how people buy and sell gear. People can buy anything they want without waiting for a store to have it. That means our consumerist impulses have run amuck and there is a glut of used gear for sale, making selling a slower process. Everything now takes longer to sell, because everyone is constantly buying stuff and then trying to flip it.
4.) Times are a changin' for musicians. The part time gig player that has a regular 9-5 to pay for his music career is the name of the game now. His or her gear needs to be small, efficient, and reliable. They are rushing home from work, need to be able to throw everything in their commuter vehicle, get to a gig where they might have to park a block away and schlep their gear, then have 5 minutes to set up for a 30 minute set before throwing it back in the car and dashing home to get up for work the next morning. Tube heads and fridges just don't cut it.
5.) The big boys and girls out there still use big ol' tube heads. When I go see real bands play, they are still using Ampeg, Orange, Mesa, and Fender heads. The difference is they have roadies and do this for a living. So the use of this equipment isn't dying out altogether, but is not as popular with local musicians.