The problem seems to be there is no barrier to entry. Say what you like about Apple's app store, at least they have standards that are enforced, and to a certain extent Google as well. Windows, and the Microsoft app store, on the other hand, suffers the same problem of quality control and lack of curation as Alexa skills. There are some gems, and Amazon have put effort into making Alexa and the Echo devices useful out of the box with their default skills/commands. I've also never had issues with the smart home skills for various devices I have around the house. However, it's a telling statistic that there are over 50 'fart' skills, [0] half of which are rated at three stars or above.
And of course, although stricter curation and quality control would fix this, it would cut the number of skills down hugely, maybe even to 1% of the current size, so the app store looks tiny and people don't bother with the platform. See also Metcalfe's law [1] and network effects...
0. https://www.amazon.com/s?k=alexa+skill+fart&crid=2KFJ9DO3N51...