The Internet was a 'bubble' at one point, and after it crashed in 2000, it didn't go away, it continued to build out. We're still using the Internet after the Internet bubble popped.
Over 40 years, that's 7-20 hardware changes, that turns into between $420B and $1.4T of ongoing investment (not accounting for inflation). The $30B that is called "infrastructure" only accounts for 2-7% of the overall bill.
This is NOTHING like fiber buildouts because the fiber lasts the whole 40 years with ZERO replacements and very close to 100% of the cost is infrastructure rather than a tiny percentage.
Conversely, for the data centers we're talking about, the cost of the things that need replacing every five years is one of the primary costs.
I'm not arguing that the current build out isn't crazy, just that AI isn't going away. Just like everyone thought the internet was a fad, but then it continued to grow (remember web 2.0). AI will morph into something useful and will be sticking around, even if we can't envision what it will look like.