TSLA owning SCTY makes about as much sense as Toyota buying Exxon-Mobil, with a small helping of 'enormous conflict of interest.'
We don't generally have that problem in the US thought, and places where that might be useful are dwarfed by the markets it's not at that point, so it doesn't make sense. Otherwise, yes, that would be a big missed market opportunity for car companies. A chance to sell more stuff, and put it all under the same financing.
That is, the difference between Tesla and the ICE automakers is that one of them has a resource (fuel) distribution problem that was already solved a long time ago, and one doesn't. That necessitates different strategies.