First and foremost, the decision to use proof-of-work was a historical one. To build a network with a proof-of-stake, the underlying cryptocurrency already needs a certain value to achieve a sufficient level of security. Second, the network must also have a high entropy, meaning that the coins must be distributed as evenly as possible so that no attacker has the opportunity to obtain the majority of the coins. This was not the case with the Bitcoin launch, so this option was out of the question at the time.Furthermore, Bitcoin places a very high value on security and also on the decentralized approach of the network. It is also helpful to read the Bitcoin whitepaper to understand why Satoshi introduced PoW. There is no fully operating proof-of-stake network yet, so the technology is experimental. Those who claim that they are operating on proof of stake are still in some respect centralist.
An exception here is maybe the PoS approach of Ethereum. Their goal is to reach an truly decentralized version of PoS and have launched a PoS chain in parrallel, but the actual hard work is still done through the PoW chain. The main problem is the so-called “nothing-at-stake” problem, with Proof-of-Stake, which means that the validator has no incentive to mine only one possible fork of the network, since unlike PoW, this does not incur any costs. Therefore, with PoS, one has to introduce additional penalties for validators who mine more than one fork, which makes it difficult to implement. Another possibility are master nodes with more authority, but this contradicts the decentralized approach of a blockain.