It's not that, it's that people were abusing it by using it for things like Plex with 100TB+ of data, which cost Google more than the revenue they got as a result. Blame the people that abused the policy. They're not a charity and can't keep an offer if they lose money as a result. Keep in mind that Google Drive data has several replicas and is also backed up to cold storage on LTO tapes, so people abusing the storage policy is actually pretty expensive for them .

They do still have unlimited data in some cases, for example with custom plans for large companies (like 50k+ employees).