It is known that creation of iron in stars causes stars to explode. But this (to my knowledge) only happens in the most massive stars. My question is why does this only happen in the most massive stars and not in other stars like our sun?

The density and temperature never get high enough in small stars to trigger the fusion reactions that result in iron. It's not even close.

 

Fusion will never progress beyond hydrogen forming helium in stars half the size of our Sun and smaller. The density and temperature needed for helium burning does not occur in those small stars. Our Sun will eventually make the step up to helium burning once it has consumed all the hydrogen in the core. Fusion in our Sun will stop there. Each step up the ladder requires ever greater density and temperature, but each step up the ladder produces progressively less energy. It's only the very massive stars that can make the step up to burning nickel plus helium to form zinc. That final step is a star killer because it is endothermic rather than exothermic.

pressure of the core.

edit-
this image is an example of a massive star

Edited June 21, 201312 yr by krash661

Like D H says, it has to do with the fact that our star is and never will be dense enough or hot enough to fuse anything past helium, let alone iron. The reason fusing iron is the last step in a massive stars life is because it is putting more energy into fusing the element that it is getting out of it, collapsing the stars core and blowing away the mass of the star in a supernova, leaving only the black hole remnant that was the core.