I'm sure it's extremely hard to balance tribes overruning the server with dinos that they leave out, causing game-breaking lag against the ability of a solo player to get anything done at all.
I'm a solo/VERY small tribe person. I have played on smalltribes, PvP ORP CrossArk, and PvE. I can see upping the breeding rates specifically being a problem on PvE servers, where players tend to build huge structures and leave dinos unpodded. Increasing breeding rates would contribute to making these servers unplayable pretty fast.
On PvP servers it's less of an issue - bases get raided, people quit and move around a lot. Instead the problem is large/established tribes being able to snowball with extremely strong dino lines. Large established tribes already have a significant advantage on PvP servers, increased breeding rates would make that gap widen faster.
That being said, I DO miss the EVO events. I've seen things like this suggested before, but would it be impossible to rotate boosts for specific things each weekend? You could even do special ones occasionally. For example:
Weekend 1: Breeding/raising baby dinos 2x normal.
Weekend 2: Taming 1.5-2x normal (Some dinos still can't get a perfect kibble tame on new rates, which is frustrating).
Weekend 3: Special weekend! 2x harvesting element.
Weekend 4: Breeding raising baby dinos 2x normal.
Weekend 5: Increased loot quality from drops.
And so on...
This seems like it might be a way to give players a special boost on the weekends without breaking the game. Increased breeding could be thrown into the mix as often as the devs want, and I think it would be fun to look forward to something new each weekend.