Less concentration of mining power is the actual decentralization so it is kind of jeopardizing the decentralized nature of bitcoin.
Why do miners stay in 2 big pools and give them more than %50 power? Even if they don't use it for evil.
Miners operates for making more money so its obvious that they can sustain being profitable only if they are under the pools where there is high chance of getting rewards and also geolocation plays a vital role in profit making so miner has to choose place the location where electricity is cheaper that is why it is scattered on few locations not all over the world.
But the fact is the Foundry USA and Antpool started to gain more miners when china restricted the mining operation that is th reason you may find the these two pools have very less total computational power compared to now.
Wouldn't it be better if total of the biggest pools are less than %50? Would you prefer 4 pools for %50 rather than 2 pools for %50?
2 or 4 doesn't make any big difference, as long as someone is having the control of 51% of total hash rate they can control the BTC network but practically they need to spend billions to make millions which doesn't make any sense that is the reason why 51% attack will never likely to be performed by someone even if they have control over 51% hash power.