I shall never understand this "Ruby is slow and difficult to parallelize so let's use Go!" mindset. People knew about the negative aspects of Ruby in advance (i.e. GIL + performance) but still chose to use it even though back then (whenever that was) there were other alternatives - no doubt without the big userbase that Ruby had thanks to Rails.
Now there comes Go which makes parallelism easy(er) but introduces challenges of its own and also has some downsides (i.e. polymorphism) which Ruby solved better - but whatever: "a good developer can always work around such challenges".
So in the end, most people are just following the hype and (IMHO) exchanging one bad apple for another...
Go wasn't an option then. Obviously the languages that WERE options, weren't preferred. The article mentions the authors lack of Java love specifically. There are plenty of other situations where Ruby (or something else) was eventually a bottleneck, and people moved to Java, or wrote their own PHP compiler, or moved to .NET version of ColdFusion... Now that Go's an option, some of the folks looking for speed are going to choose it.
