You don't have to. The tools which worked 10 years ago still work today. The tools which worked 5 years ago still work today. No one forces you to switch to the new hotness, people choose to.
This is not just about tools still working; it's also about maintenance, evolutions, bugfixes, libraries, available workforce etc. If you happen to use an unpopular tool, then you can't easily leverage other people's work and it's harder to find qualified engineers to work for you.
Exactly, which is why I'm still using Knockout, it's been around for a long time (for a javascript library), values backwards compatbility and is still developed (only a few developers but they are all committed).
It's also just got a lot faster (3.4 had huge speedups) supports HTML5 components and supports IE back to 7 (while that's not a requirement for me it's nice to know the tools you have will work if you need them to).
There are features in newer libraries I like but taken in balance I like been able to grab the code I wrote 2 years ago and have it still work with knockout's latest version, to me that is it's killer feature.
