FWIW i am Danish and almost all of our public IT projects are done in .NET, almost always the reasoning is "more developers, more mainstream, less lock-in". Our IT projects are always hilariously belated and more expensive than budgeted. More often than not the same contractor (one of 5ish big corporations) keeps getting the same contracts from the same departments because they have pre-existing knowledge of the system they previously built (hint: this is lock-in). Now, the last part is changing somewhat due to EU tender rules, which I think Norway also abides by (they are not in EU, but are committed to complying with most EU laws)
We're incentivized to work this way because that makes the customer feel safe. Which is how we win contracts.
In fact, I think what you suggest would be an extremely short-sighted "strategy" for a consultancy. Sure, you might get the next contract working this way. But once the customer could get rid of you they would, and they would never hire you again.
At Vy, Elm is used for frontend, Java and Kotlin for backend.
Kotlin in the backend isn't a mainstream technology choice either.
So far we are not dissapointed, and in my opinion Elm is on its way to become mainstream because of these things.
Also, as learning Elm is quite fast - I don't think the vendor lock-in is a very convincing argument.