The chips needed to produce one-to-many USB-C hubs essentially do not currently exist.
Some of the same complaints are outlined here:
None of these USB-C “hubs” actually give you more USB-C ports.
There is supposedly news for 2019/2020 that suggests hub chips may be coming soon:
Update (2018-07-30): Accidental Tech Podcast reports on a rumor that next year Intel will finally ship the chip that’s needed for making a USB-C that adds additional type-C ports.
We've heard from an anonymous person that Intel is finally releasing a hub chip for USB-C next year. We may not see products based on it until 2020.