I think it is a few factors...the hobby has gotten prohibitively more expensive and huge inflation to everything. So people have to decide where they want to spend their money.
Also, people have less time now to take care of their tank. They have to go back to work, work more hours or travel for work. Naturally, the tank suffers and it requires even more time to fix it, which you don't have. It's a feedback loop until you just decide to leave the hobby.
The learning curve got a lot steeper. Today, there is information overload. If you are a newbie, you don't know what is BS and what works. There are simply too many options right now for everything. Back in the days, you got 1 brand of salt, Instant Ocean. You used the swing arm salinity checker. The only rock option is live rocks. Basic controllers with pH and temp only. Lights were either MH or T5/CF. The dosers were your hands. LOL.