They are perhaps #1 and #2 in the "enterprise" market share, but in no way are they overall #1 and #2. Not even close. Which web app or startup uses them?
Well with that question you neatly define the bubble that you inhabit.
https://db-engines.com/en/ranking ranks Oracle at number 1 and MS Sql Server at number 3, their method being a broad range of statistics based on job offers and web search statistics.
https://survey.stackoverflow.co/2024/technology#most-popular...
You asked for one via Which web app or startup uses them? :)
Also, 90% of the web are either cat memes and stupidly insane things like social media and video streaming shit platforms