Popularity is important if you want to hire developers - developers are generally less interested in moving their career in a different direction than the industry trends.
Popularity for frameworks is also important if the framework needs adapters to enable third-party libraries to work with the framework. Depending on how opinionated the framework is, the friction in embedding libraries may hamper productivity indirectly.
If you're a one man band, then it's definitely less important. If the framework is a really good fit for the job, likewise. Otherwise, there's safety in numbers.
Popularity for frameworks is also important if the framework needs adapters to enable third-party libraries to work with the framework. Depending on how opinionated the framework is, the friction in embedding libraries may hamper productivity indirectly.
If you're a one man band, then it's definitely less important. If the framework is a really good fit for the job, likewise. Otherwise, there's safety in numbers.