League of legends is supposed to be a strategic, teambased, skill game. And changing the map for the rest of the game seems to give more luck than strategy, I'll explain why.
When an elemental dragon spawns in a game, the map is changed in 1 of 4 different ways. Having different effects. If you don't know what the 4 drakes do yet I suggest reading the post I've linked above. A lot of champions have unique interactions with the terrain, here are some examples.
Kayn - Kayns E allows him to pass through terrain, allowing to gank from multiple angles.
Illoai - Illoai's passive tentacles form next to walls
Taliyah - Taliyah's passive allows her to surf of walls for faster movement speed.
Rengar - Rengar can jump out of bushes
Camille - Can grapple to walls and jump off of them too.
These are just a select few that came into my head when writing this post. Now I'll tell you where the problem is.
Some champions will be put either at an advantage or disadvantage when the map is permanently changed. If you're playing against a rengar and the Ocean dragon dominates the rift, he just got ALOT stronger, simple due to a dice roll. Cloud drake? Hecarims passive gives him bonus ad the faster he is, now he gets more AD for doing absolutely NOTHING. Playing against any sort of champ that relies on terrain? Well Fire and Mountain drake will either buff them or nerf them, all because of a dice roll.
Too many champions are affected by the map around them, and by changing the map every game, you are putting them at a disadvantage/advantage for doing NOTHING. This game is supposed to be interesting with teamplay, mechanics and strategy; not with some silly dice roll that doesn't need to be implemented, you can keep dragons the way they are, no one really had a problem with the map (atleast I don't think) but adding a luck based feature will not improve the game and will only cause more frustration and RNG to this game.