Ethereum itself can be used as a decentralized storage system, and in fact it is when it comes to code storage in all the smart contracts.
When it comes to large amounts of data, however, that isn't what the system is designed for.
At the time of writing, the Ethereum chain is around 350GB, and every node on the network needs to be able to store all 350GB of data.
If the chain were to expand to large amounts of data (say 5TBs) it wouldn't be feasible for all nodes to continue to run.
Also, this can get incredibly expensive to deploy new data due to the size.
Due to these constraints, we need a different chain or methodology to storing large amounts of data in a decentralized manner.
When looking at decentralized storage (dStorage) options, there are a few things a user must keep in mind.
Persistence mechanism / incentive structure
Data retention enforcement
Decentrality
Consensus
Arweave is mentioned in all 4 areas...
https://ethereum.org/fi/developers/docs/storage/Also, when ETH2 does eventually release, im 100% confident Arweave will play a vital role for ETH'S data storage.