The primary reason to not use PoS is simply having an ongoing cost and expense external to the network.

So when we quantify mining revenue and staking revenue, what we usually do is quantify risk. A miner must make an investment and has an average expected return, their exposure is partly to volatility of bitcoin for example and to energy prices and what not. A staker of ethereum for example doesnt really have this, their risk is only in making mistakes, server downtime, opportunity cost. The slashing rates and things are designed with incentive in mind primarily, and expected risk losses are downstream of those decisions. But we always quantify it in terms of risk, but theres another big side of this: ongoing expense.

There is a minimal ongoing cost to staking. Make your initial investment, get high uptime on your node, youre good. A miner has an ongoing cost, in energy, in big facilities, in hardware depracation. Additionally, a miner has an ongoing cost external tp the network. This os a very big thing. they have to buy energy, hardware. A staker doesn’t have anything like that, their activity is entirely internal to the network.

There are major game theoretical implications to these big differences. There are pros and cons, but all in all I and most people, and particularly in the Monero world, think PoW handily wins out.