Fun story:

I built BetaList 16 years ago which was one of the first "product discovery" platforms. Years before Product Hunt, etc.

I manually reviewed every submission and unfortunately often I had to tell founders that their startup didn't qualify to be included. Almost everyone would (understandably!) argue their case, but as volume increased I couldn't afford to go into a deep argument with every single founder.

That's when I made https://submit.co a site similar to OP's. The idea being that instead of say "No, we will not feature your startup" I now gave them an alternative place to put their energy.

Initially it was mostly a list of tech blogs, but as more product discovery platforms popped up, I started adding them too. In a sense, I was promoting my competition but it was exactly the startups we couldn't list any way for one reason or another.

Eventually that list of "places to submit your startup" got so popular (and copied everywhere ) that it started driving traffic back to BetaList. (I included it at the very top of the list).