Seriously RIOT use to do holiday map skin why don't we have maps that look different maybe even different jun monsters but same stats and buffs same concept of the game just a new LOOK PLEASE IS THIS REALLY THAT DIFFICULT TO DO??
Time, effort, money, testing, clarity.
The current map is built around the current abilities and champions, to allow there focus on clarity, it's going to be damn near difficult to formulate another map, whether it's a Holiday wonderland or a Dark Void to fit with the current abilities and champions. Those texture rebalances weren't half assed visual updates they were done so everything blended together seemingly.
And that's only 1 of the problems, they'd have to go through and make all the new quality textures, make optimizations and fix a slew of things, when there time can be better spent balancing the game, fixing bugs, or releasing skins/champions.
Edit: Idiots that downvote factual evidence is hilarious, you don't make it any less true just because it makes you mad, all you do is hide the truth under piles of more garbage comments.
Dota 2 has had weather changers for a few months and they just rolled out a desert theme. Oh and you can activate these at your digression without affecting other players.
I remember the old winter summoners rift...
Fun fact the snowballs that the snowman would throw at you would activate the cooldown for 
To be fair, they did change the Crystal Scar for Shurima and the Howling Abyss for Bilgewater.
I think we will get Rift changes with events in the future.
Started playing in S3 during Lissandra patch so I have no memory of this :( Either way given that it's supposed to be almost 80 on Christmas Eve on the east coast I don't think it's very fitting.
they're waiting on the summoner's rift visual update... oh
It's a huge amount of resources to revamp a map
