Because SQLite has 10k requirements that wouldn't even cross your mind to write down, but 80% of which are useful to you.
This isn't anything new or particularly interesting. It's the entire basis upon which ILP demonstrated generality. A metatheory to synthesize 10 trillion rules isn't even scratching the surface of what you can reasonably do. The key was finding out the tractable semantics for actually computing it in reasonable amount of time, which right now is looking decidedly like informal semantics was the answer the whole time.
https://www.youtube.com/watch?v=V_qzqY1bb7I your sufficiently advanced code generator may generate you a high quality database system for some measure of quality, but it will not have SQLite's reliability over the extremely long tail of edge cases proven through its testing and use in real life
That's before we get into the entire non-linearity of agentic systems introducing massive decidability problems on this in the first place. A little bit of epistemic humility please.
The assumption you make is the classic LLM mistake of thinking writing code === building software.
To cite your example SQL has had its tires kicked a lot it’s seen things you can’t even imagine thanks to being used millions of times by millions of people. It’s hard to just replicate all that iteration, learning, mastery, and process. If you reinvent it, users will encounter the dumbest bugs over and over and over. Sure you’ll fix them, but you’re now embarking on this big thing that SQL and others already did.
If you love the problem space definitely do it - go full steam ahead - especially if you’re actually innovating and doing things better, but don’t be fooled into thinking anyone can, or should with every side project.
The new struggle is focus, what not to build, I almost have the purely opposite view of instead of using LLMs for grandiosity, only using the LLM for tedium and making sure it doesn’t do anything too much that I haven’t planned for or want to do. I drive the thing, so every new project is still my time and energy and focus.