It's never too late, but the problem are :
1. Decentralized pool (such as P2Pool) already exist, but it's barely used. It means miners don't care about decentralization or too lazy to configure their miners for P2Pool.
Depending on how they get into mining, they may not even know it exists. That's the problem, with all the informative sites just regurgitating the same info. People mostly wind up on a Bitmain owned/controlled/partnered pool or Slush. The bigger hey get the harder it is for people to think about trying out smaller pools spreading the hashrate out but increasing variance in reward frequency.
2. Assuming the community/developer agreed to change into PoW which prevent pool, miner & pool owner most likely will stall/prevent it from happening.
If discussions ever got far enough to consider moving away from POW and people were actively considering this. You might see people open their eyes and branch out to other pools to spread the hashrate. If for no other reason than to not rock the boat possibly having a negative impact on the overall market.
The bigger the pools the highest chances of hitting a block,
They will hit them more frequently, but the miner earns a smaller fraction of each block because the reward is spread so thin. That's why in theory these miners can earn the same amount at any size pool over a long enough period of time. Ideally you want to be at a pool that is large enough to expect a block every Difficulty Adjustment Period. This way you might hit fewer blocks but you earn more BTC per block. So really the lowest fee pool, is the best choice assuming they share block rewards.
And at the same time they should understand that if they choose pool, which is very close to 51% they they won't earn anything and even lose everything they got. I know that miners are earning money but I don't think they are so retarded that they would harm themselves.
Just because someone reaches 51% doesn't mean everyone instantly loses everything. If they began doublespends then yes the market would be in trouble, loss of faith is huge. Like I said above if we ever got close enough it would become a frontline issue and people would actually have to make themselves aware.
That would be interesting to see if the majority hashrate holder would try to convince the world to make them the central authority.