These people are often labelled as the "pragmatic". They also lean towards having a more general scope of knowledge and thus often lack a "speciality".
There are also those that simply wish to solve the problem in the "best" way possible, and will use whichever stack gets them closer to that ideal solution.
disclaimer: purely based on my experience/opinion/perspective.
In the past I work almost exclusively within the .NET ecosystem (only some small projects in Java, Python, etc.). When I took up learning Scala, I decided that I want to immerse myself in full-time Scala development and started to look for Scala-related roles.
If you present yourself as just a bunch of TLAs you're effectively selling yourself short. Put bluntly, if you do that you're presenting yourself as a code monkey who turns other people's ideas and solutions into that nasty computer code the people who do the "real thinking" can't be bothered to deal with.
Besides, your favourite stack today might fall out of favour tomorrow. If you invested a disproportionate amount of time into learning all the intricacies of that particular stack you might have wasted a lot of time.
Being able to analyze and solve problems regardless of the toolset is a skill that likely will never fall out of favour.
Totally! I definitely wouldn't want to work in something like, say, Pascal, but my all time favorite job was at a startup using Java, of all languages.