Cryptocurrency networks are not created to mine or stake and get rewards from staking or mining.
I did not say this.
Please don't arbitrarily to use the phrase "alternative to mining cryptocurrency".
Yet proof of stake is an alternative to proof of work? I would define 'mining' as confirming transactions and maintaining the blockchain and distributing rewards to the 'miners'. Proof of work and proof of stake both do these, so proof of stake is an alternative to the traditional 'mining' of cryptocurrency through proof of work.
Both have pros and cons. PoS coins are more easily to end with deaths.
For coins that have massive APY and are built on PoS, yes (But you should not be buying these shitcoins in the first place). But this is not true for coins that have real uses and a small, sustainable and realistic APY.