Because it's hard. Also technical debt moving from Eth 1 to 2 makes it harder.

My guess is another blockchain will execute PoS better because it won't have tech debt.

The original plan would have been hobbled by technical debt. They were going to implement the core algorithm as a smart contract on the old chain. It would have supported a much smaller number of stakers and shards.

In mid-2018 they threw out that plan, choosing instead to implement PoS as an entirely separate chain, integrated with sharding. This entailed a delay of over a year, but it meant a minimum stake of 32 ETH instead of 1500, and an overall much more efficient and scalable system. There are three main phases, the first being the core proof-of-stake "beacon chain," which is currently running a multi-client testnet.

There have been various proposals for migrating legacy Ethereum into all this; here's the latest: https://ethresear.ch/t/alternative-proposal-for-early-eth1-e...

Cardano is PoS and released its testnet last month.

Tezos is another.

Cosmos is PoS and released its mainnet in March.

A Proof of Stake consensus for a public blockchain like Ethereum has different requirements and is substantially harder to execute than for a permissioned network.

Definitely agree, although it’s important to clarify that Cosmos is not permissioned. Anyone can start a validator and join the validating set.

Proof of Stake has a separate set of problems to worry about than Proof of Work. It's a solution to some of the scaling problems, but at the expense of some security.

As with all engineering, it's a set of tradeoffs.

Proof-of-stake is cryptocurrency's fusion power: perpetually "less than a year away"; it's the technology of the future and always will be.

What are the problems with current PoS systems? Not being glib, seriously interested as there are at least a few that implement some kind of Pos (for example dPoS with Ark)

Permissioned networks are a very much easier setting to design a consensus protocol for than public ones.

Describing a consensus algorithm as "Proof of Stake" simply means it uses some kind of stake to secure its decisions, this doesn't say anything about the assumptions it starts from.

Existing "PoS" blockchains don't have the same decentralization goals as Ethereum.

> Existing "PoS" blockchains don't have the same decentralization goals as Ethereum.

What about Cardano and Tezos? aren't they decentralized PoS blockchains?

And Cosmos

“Existing ‘PoS’ blockchains don't have the same decentralization goals as Ethereum.”

What makes you think this?

How is Ark less decentralized?

From my understanding, the issue with PoS is that if a chain forks you can mine both sides without penalty. A consequence of this is that if someone wants to retroactively create a fork that starting from a block a few years ago, then people could do a few years worth of mining of this fork in an instant. And it wouldn't be possible to tell these two chains apart cryptographically. With PoW it would be computationally expensive to pull such a stunt.

Not exactly, it's here and technically working in multiple production blockchains, it's just less secure than Proof-of-Work. So it depends what your definition of "works" is.