play Fixed map games anymore?
There was a time people played fixed maps regularly?
Anyway, the biggest reason is that random is different while fixed maps benefit the player who is experienced on that map....
Fixed maps aren't generally any more balanced than random maps (the size of militia on uncolonized worlds as well as the number of extractors at a planet are still random), so a fixed map actually has very little to offer over a random map....
I'm not saying the random maps are amazing, but when the number of played games you have is in the hundreds or thousands, fixed maps can get boring....