I think your obvious answer is wrong. The fact is that modern smartphones are walled gardens with very large, powerful gatekeepers who want to protect their duopoly. The original impetus behind locking down the operating systems on smartphones was security but it evolved into a perfect way to ensure control over their market. There are no generic PC clones in the cellphone market, only small hobbyist or niche products that barely work. A+G encourage programming for their OSs only in so far as the output of such an activity can be sold on their app stores where they can take their cut and still retain absolute control over what gets installed.

In regards to plugins, someone has to write them. Even if the people writing those plugins use LLM tools to assist them they still need to know how to put software together and how to manage all of the services that those APIs talk to and how to scale their infrastructure along with user growth.