Sorry for the delay.The easiest way to explain this is nuclear stability. So when we talk about decay, half life, nuclear stability - those which are way more stable are going to have considerably longer half lives before degrading from the sample(of whatever you are looking at).So if you look at it from a stressor standpoint, those which which are considerably more unstable are going to have shorter half lives.
Alright so I did the best I could to gather more information. Some of this is literally just nature of the isotopes and really can only be explained by nuclear physics, that neither I nor my friend who is a PhD in chemistry from a prestigious research school can explain.When an isotope is unstable (thermodynamics) it doesn't mean it will be a fast (kinetics) decay. Some isotopes have LONG half lives and some have very short ones. the half life can't be affected by things like heat, pressure, etc. it's intrinsic to the isotope, meaning it just the nature of the isotope, some just decay faster than others. Nature of the isotope/element involved which would need specific nuclear physicists to explain(assuming they could do so in laymans terms)