[Obi_Juan_Kenobi]

Mining economics depend on the mining reward. It doesn't get bigger if more people mine. The rewards just get spread out over more/larger participants until profits are tiny via difficulty adjustments.

The mining effort depends simply on the reward, and the reward is calibrated to the security needed. Bitcoin is highly secure, but the security model is essentially 1:1; if the network is secured with a billion dollars of mining effort, it will cost on the order of a billion to attack it. So it's expensive.

PoS can have a better security model, maybe 1:100 against network attackers. So you can reduce mining rewards and maintain a given security level.