Yeah, I didn't like any of the 19" or 20" options to be honest (just went with the cheapest 20" ones to replace later). The good news is there are a lot of after-market options at this point. And with the release of the Taycan CT, they added some CT-specific ones that will probably fit the regular Taycan.
To be fair, a lot of those are the same wheels in different colors. The Taycan has color options in a separate drop down. 911 is this way also. Just the separate wheel designs are shown with color options separate.
That said, I would agree that it’s not the best selection (and still fewer overall).
I think the fundamental problem for Porsche for the Taycan is range. If Porsche makes available less aerodynamic wheels, then owners who experience reductions in range will complain. This isn't an issue for the ICE Porsches, as people don't really care if their MPG drops because of their wheel choices. The problem is less pronounced in the larger wheels, basically because the large wheels themselves already impose a range penalty (supposedly ~10%) that is not easy to overcome with wheel aerodynamics. But the drop off in a 20" or 19" wheel is likely to be noticeable (supposedly ~3%).
Thus, if you're Porsche, you're not keen on making available wheels that impose this penalty. Better to let people buy third party and live with whatever range impacts they have assumed.