Yeah ? like the tons of photos they harvest from people. Most of the progress they did in training computer vision is based on that. Should I build facebook or google to get access to it ?
What about language modeling ? They have access to conversational data and billions of search queries, both of which there is no way to access them from outside.
What about health ? Well if I'm not somehow working with some big pharma how could I access this kind of data ?
I can go on and on. The point is, yes I can crawl the web, but what "web" is there left ? everything is locked behind paywalls and private clouds. If the real vision of an open internet was fulfilled, all data generated on it would be accessible to crawl indeed.
I'm not saying it's not possible to get data and use it. I'm saying you cannot get the kind of data only monopolies have and you will never be able to compete with them.