As another not-physicist who is interested in physics, I've found the articles/explainers at Of Particular Significance very helpful. There are a few on particle decay, and I think that these two provide a longer answer to your questions:

Most Particles Decay — But Why?

https://profmattstrassler.com/articles-and-posts/particle-ph...

Most Particles Decay — Yet Some Don’t!

https://profmattstrassler.com/articles-and-posts/particle-ph...

Neutron Stability in Atomic Nuclei

https://profmattstrassler.com/articles-and-posts/particle-ph...