There are projects out there with real use-cases. However, most investors are there for profit, not to support the project. Investors come in and out of new projects taking all the profit they can while they can, and that is how the market goes. Only a few people are doing their research and investing for real technology.
You are right as long the as project is new and if possible they can take all the profit out of it before shifting into a new defi project where they would do the same thing and that makes the project more vulnerable from whales that is why many start up defi projects innovate and implement some features where whales are not going to exploits or manipulate the market price, one of those the Speculative or Priceless AMM where it contains the price volatility of a certain coin.