It isn't a core tenant of PoW that the resources needed to participate are hard to get, it just so happens that if it is profitable to 'mine', the hardware needed will become scarce. That actually creates a problem, much like in the Bitcoin PoW algorithm, that its easy for the hardware production and ownership to become centralized.

PoW also requires large energy consumption as participants will inevitably enter a race to compute the fastest.

PoS has the benefit that you still lock away capital, much like in PoW, but rather than backing that capital by money put into hardware and electricity, you cut out the middle man and base the capital off of the value of the network token.

Pos also has added security benefits. Vitalik Buterin explains this very well: If someone attacks a PoW blockchain by getting 51+% of the hashing power, the network's only response to recover from the attack is to change the hashing algorithm. This will likely force the network to abandon ASICs since hardware wouldn't exist, and move (at least temporarily) to general-purpose CPUs/GPUs. As soon as the hashing can be done with general purpose computers, the game is over, and the attacker can attack forever without any extra loss of capital, other than electricity.

PoS has the benefit that the network can simply cause the attacker to lose their funds and no longer have a stake. If the attacker wants to continue the attack, they have to buy more of the network token to be equal to 51% of the staked value. This will cause a price increase. Each time the attacker attacks, the network will force them to lose their stake, and their money. The attacker won't be able to keep this going forever.