why should I even care if language X is on the rise, or decline, if it's user base or kloc is huge or miniscule?

There are different reasons for different people.

Job seekers want to know what to learn so that they can be employed. Your favorite language may be great and all, but it won't matter if no one will hire you to write in it.

Employers want to know how to implement their next project. They want a language known by many programmers so that it's easy to find people to work on the project now and in the future.

Hobbyists want to know where they can get support. They want a language with a strong community and good documentation so they can teach themselves and get help when they're stuck.

There are still other reasons for other people, probably.