For indie devs it makes sense, community feedback will help them as they can't possibly do all of the testing and brainstorming themselves (particularly with a single dev). Other than that? Yeah, it's a cash grab.

It's intended as an open collaborative system. Small developers get an early injection of cash to fund further development. They can also get continuous feedback, from the community, as they develop. For smaller companies, this can be critical to help keep them on the path that makes the game better.

In turn, the community gets to have a say in how the game is shaped. They also get to play it early and watch it grow. It's often also cheaper to buy early.

When used right, it's awesome. Unfortunately it gets abused a bit right now. Bigger companies using it as a bug fixing tool is problematic, particularly when priced at full price. Also some (intentionally or not) do a "take the money and run".

7 Days to die, valheim, and satisfactory are examples of early access done right.