I completely agree.
It does seem that startups sometimes go out and raise money simply because it's the expected thing to do. And with the cost of getting a product to market and a business off the ground so incredibly low these days there is much less of inevitable need for VC than there was, say, in the 90s.
That said, raising capital can be incredibly useful for a company. It can fund initiatives that otherwise simply wouldn't be possible with cash on hand. And traditional lenders might be hesitant to give loans to a very young organization with few assets.
I would imagine there are various creative ways to handle this A co-op could always sell shares to an investor if they decided to not be 100% worker-owned. And a co-op could always decide to seek a traditional exit event at some point if they wanted to (there are plenty of publicly traded coops). Or you could structure some kind of joint venture. I imagine though that the biggest problem would be that most investors wouldn't want to take on the added risk of dealing with an unusual corporate structure if they didn't have to.