I think that's not the reason. NoSQL rocketed in popularity on the back of adoption by a few large companies with scale problems that had to abandon relational

I think that's not the reason. NoSQL rocketed in popularity on the back of adoption by a few large companies with scale problems that had to abandon relational databases due to scale issues. If the requirement is to serve very high low-latency throughput to back something like shopping on Amazon, then relational databases and SQL in particular aren't very helpful. You know your data access patterns up front, and can optimize your database to support exactly your API's access patterns. Ad hoc queries on the production database are prohibited, data analysis work gets done with some kind of ETL pipeline, and the choice to trade off any part of ACID for more throughput and lower latency is a no-brainer.