People are building toy demos in a day that are not actual useable products. It’s cool, but it’s the difference between “I made a Twitter clone in a weekend” and real Twitter.

1 - companies are deploying real products internally for productivity, especially technical and customer support, and in data science to enable internal people to query their data warehouse in natural language. I know of 2 very large companies with the first in production and 1 with the second, and those are just ones I'm aware of. 2 - you are conflating the problems of engineering a system to do a thing for billions of users (an incredibly rare situation requiring herculean effort regardless of the underlying product) with the ability of a technology to do a thing. The above mentioned systems couldn't handle billions of users. So what? The vast majority of useful enterprise saas could not handle a billion users.