Ruby is fantastic for writing a-lot of code quickly. But it has terrible performance, and is has terrible maintainability characteristics (I recall doing global file system searches to find the file that defines something that my code requires, which is brought in by another require, and then another).
Performance sometimes matters. If one's app requires 20 VMs in Ruby, but only 2 VMs in Go or C++, then the cost difference can be substantial.
Also, Ruby - while 20 years old - is surprisingly immature. E.g., a few years back, I wrote a multi-threaded program in Ruby. It didn't work. After days of scratching my head, I discovered that while Ruby used native threads, it had a global interpreter lock, forcing the native threads to take turns. Maybe they have fixed this by now. My program needed true concurrency, so I had to re-write it using processes. Gosh - Java got threads working after the first two years.
Firms that really know how to maintain large codebases have also discovered that type-safe languages are very effective for maintainability. Check out this post: https://medium.freecodecamp.or... . I myself have experienced this: I once translated a fairly good sized codebase from Ruby to Java, and in the process discovered a large number of potential bugs - thanks to Java's type safety. I have found that when I refactor Java code, I introduce zero new bugs, but when changing Ruby code, the only thing that prevents new bugs is a large suite of unit tests. Thus, writing in Ruby _requires_ that one write comprehensive unit tests. I personally don't use TDD - I use ATDD, so my focus is on acceptance tests, not unit tests. Ruby _forces_ me to write unit tests. I don't want to be forced to work a certain way.
I am not bashing Ruby - I think it is great for some things - but people (like those at Google) have come to understand its shortcomings.