Right, a few users don't make something mainstream. Big companies have thousands of developers - even non IT companies - that someone inside some big company uses a programming language doesn't make it an indicator for widespread (most people use something -> mainstream) usage.

Mainstream: large relative and absolute numbers of users.

For example the Porsche Taycan (-> Microsoft) is not a mainstream car, even though Bill Gates has one and Porsche is an incredible profitable company. https://www.economist.com/business/2019/09/12/porsche-is-sma...