My two cents about the biggest problems of Scala:

• Regarding the “big companies do not trust Scala”. I would say that the problem is especially that there is not one big mainstream company (from the GAFA) that publicly adopt and support Scala. Look at the rise of TypeScript (backed up by Microsoft and Google (via Angular)), Swift (appeared out of nowhere by Apple), Kotlin (official support for android, again Google)… In a dream, Facebook (the “last” one) would adopt Scala/Scala.js for React…
• Regarding “steep learning curve”. Well, I would say it’s rather the legend that Scala has a steep learning curve. For the overwhelming majority of a developper’s day to day job, Scala is quite simple IMO. Of course if you try to understand the source code from day one, yes, you’ll have a steep learning curve :)