There was a certain amount of tandem track sprinting for many years ( triples and quads as well pre-war).
I rode a few tandem sprint events, including the National Championship.
Unfortunately tandem racing was dropped from the Olympics, and subsequently the UCI worlds. The reality is that funding for events is about Olympic, and at a lower level Worlds, performance.
A secondary consideration is that the new indoor smaller, tighter Velodrome’s aren’t as ideal for tandems as the older outdoor tracks, ( although I know some might disagree).
When Andrea Ingram was the Coach at Manchester she put on a tandem omnium; she was an enthusiast, but she moved on. Newcastle track had an omnium as well at about the same time.
On the track, everything flows from the Olympics - because those are the performances that fund the sport.
There is, of course, still a continuing amount of tandem, and even tandem trike, time trial racing.
Tandem road racing would depend on interest, in something that doesn’t have an obvious progression, and someone building suitable tandems ( Mercian build racing tandems, but I’ve seen few other current ones) . Personally, I’d imagine a fair few serious crashes as well ( 3 or 4 up tandem track racing was often pretty physical, I’ve still got some scars!)