I am a massive fan of the Superman franchise and perhaps surprisingly, a lot of my fandom leans towards the live action adaptions rather than the comics.
However, I am familiar with the Superman comics and the established lore throughout the years. Now having recently picked up Lois and Clark on DVD (which I last saw when I was a kid and is still surprisingly good!) I'm reminded of the constant inconsistencies that arise whenever a comic book is made into a live action adaptation. The fact that Krypton is a blue planet with red continents is an example from the show - no big deal, but it goes against any previous incarnation of Krypton in the comics or indeed, the movies.
This then got me thinking about any MASSIVE plot holes throughout the Superman franchise and I arrived at a conclusion - Kryptonite.
Now you'll have to forgive my somewhat elementary knowledge of astrophysics, but I'm under the impression that celestial debris such as asteroids and meteors, etc cannot exceed the speed of light - therefore it is extremely unlikely that they would make it to our galaxy from Krypton's by the time Clark Kent has become Superman (or earlier depending on series or adaptation)
Now it's a given that Kal El's spaceship was designed to reach massive speeds far beyond the speed of light in order for Kal El to make it to Earth whilst he was still around toddler age and in most of the adaptations of Superman - Kal El leaves Krypton well before it explodes, so there is no chance of his spaceship dragging the Kryptonite within it's field (subspace Trek crossover?
) This then brings us to Smallville...
A work of brilliance if I may say so myself, but mainly because Smallville takes place in contemporary times where orbital satellites, probes and galactic observation technology is in abundance. So we are given the meteor shower which was probably pieces of Krypton debris dragged by Kal El's ship (within the > c field) to Earth in order to cover up for the fact that an alien spacecraft was landing in rural Kansas. So with that in mind there is an explanation for the presence of Kryptonite within the Smallville series, but none for any other of the adaptations.