This has been my experience, too. But I think it's wrong to jump to the conclusion that because going too far and having to learn too much is a bad use of time that you should just stick to one or two things. This is black-and-white thinking and I think in this case, your response should be in the context of the problems you face and the career you are building.
We do need to move along with technologies if we want to stay relevant. But you need to know what's a fashion and what's worth adding to your skillset. After leaving University I mainly knew Java but I learnt PHP and JavaScript because I wanted a web development job; later on I felt that none of the cool startups were using PHP and all of its warts had become very apparent to me so I picked up Python which seemed a lot more elegant. (However this was more a case of fashion that gave me access to higher-impact and higher-salary jobs. My actual needs to code in a general-purpose language with nice libraries isn't a worthy goal in itself.)
Currently I am working entirely in Node.JS and I don't consider myself to be drinking the Kool Aid because it made more sense to stick to one programming language and I needed long-running processes. I do have to be careful to not add too many libraries, however. There is so much activity in the JavaScript world currently.
I say you should focus on your career and wherever you see that leading you. To a certain extent programming languages and libraries will come and go (they will coalesce on principles so this is worth paying attention to), but architecture remains the same, social structures and positions remain the same, and sales remains the same. Apply yourself where you can see the maximum potential for personal growth and personal growth that doesn't slip (as it will when you have spent 20 years programming using the library X and everybody else switches to Y.)
We do need to move along with technologies if we want to stay relevant. But you need to know what's a fashion and what's worth adding to your skillset. After leaving University I mainly knew Java but I learnt PHP and JavaScript because I wanted a web development job; later on I felt that none of the cool startups were using PHP and all of its warts had become very apparent to me so I picked up Python which seemed a lot more elegant. (However this was more a case of fashion that gave me access to higher-impact and higher-salary jobs. My actual needs to code in a general-purpose language with nice libraries isn't a worthy goal in itself.)
Currently I am working entirely in Node.JS and I don't consider myself to be drinking the Kool Aid because it made more sense to stick to one programming language and I needed long-running processes. I do have to be careful to not add too many libraries, however. There is so much activity in the JavaScript world currently.
I say you should focus on your career and wherever you see that leading you. To a certain extent programming languages and libraries will come and go (they will coalesce on principles so this is worth paying attention to), but architecture remains the same, social structures and positions remain the same, and sales remains the same. Apply yourself where you can see the maximum potential for personal growth and personal growth that doesn't slip (as it will when you have spent 20 years programming using the library X and everybody else switches to Y.)