OpenAI's goals are (1) make money and (2) generate positive press coverage about OpenAI. (They make statements about wanting other things but that's mainly to help them achieve (2).)
Prioritizing people with concrete project ideas helps them in both areas: they're more likely to convert into paid customers down the line, and they're more likely to generate "OpenAI technology is now being used for X" press releases.
I think there's a fair argument that groups attempting to make a specific product are more likely to drive platform development than random individuals who just want to noodle around. This isn't to say that the more individual experimenters won't drive development too, just that when you're dealing with limited resources you do have to make some decisions about allocation.
Just framing it in terms of money and "generating positive press coverage" is a little cynical IMO. Is prioritizing any cool use cases of their technology that push the boundaries of today's technology to create real use cases besides "haha look I can make GPT3 parody VC Medium/LinkedIn articles" just press optics? I don't think so but can also understand the concern especially given this article is about democratization.
Prioritizing people with concrete project ideas helps them in both areas: they're more likely to convert into paid customers down the line, and they're more likely to generate "OpenAI technology is now being used for X" press releases.