It's partially marketing and partially support-based. React and Angular were released with a lot of fanfare by Facebook and Google respectively (and with a lot

It's partially marketing and partially support-based. React and Angular were released with a lot of fanfare by Facebook and Google respectively (and with a lot of documentation) after being used inhouse. This meant that there was already a decent number of developers familiar with the framework, already proven as "web-scale", and indicated that there would be good support for it going forward. This meant that it was an easy sell to CTOs. Mithril.js came out after React and was released by a lone developer. While it was well-documented it didn't have the amount of documentation as react and angular, was supported by one developer and didn't have a large install base of existing users. I'm starting to see it being used by more companies but it's certainly a harder sell than angular or react