Sure.
So first off - we don't control the Starlette code base, which means breaking changes can happen without our discretion. This happened with the switch of the test client to httpx, which while pretty cool, also posed some difficulties for us.
Secondly, we no longer need Starlette because we actually implemented the complex parts on our own - we have a completely different routing level. We have our own requests, we also use a different typing (asgiref based etc.) which is no longer compatible.
Finally, the parts of Starlette we do use, we cannot change or optimize and are bottlenecks for us. I would much rather have our own response classes and the few middleware we have from there, and have the ability to modify and extend them into our patterns.
From my PoV the only real reason to keep Starlette around is that it gives Starlite more credibility. But Starlite is more established now and we have a significant community. I think we are reaching a point were this is no longer required, and in fact it works against us- Starlite is not merely a "wrapper" around Starlette. It is in fact about 2 to 3 times larger and significantly more complex.