It isn't just about the hype, it's also about the exit scam.

Most defi things are constructed in a way that makes them a free option on shitcoin vs btc price.  You put up some shitcoin to get loaned Bitcoin.  Shitcoin price tanks?  Default on the loan, lender gets worthless shitcoin and you laugh off into the sunset.  Shitcoin price moons? repay the loan and get your shitcoin back.

Most are also constructed so that some centralized party (or worse, some Sybil attacker) can just walk off with the coins.

Legitimate use for these things is essentially zero, the only one you see people promote in any detail is the use of loans to avoid capital gains tax but that *does not work*, because that activity is a "constructive sale" as any clueful accountant could tell you.

These schemes get pumped at the promoters expense to attract suckers to buy otherwise worthless associated tokens and to bring in masses for the exit scam.  It's like bugs to a bug zapper.