It’s to do with having a consistent income for them. Taking a hit to monthly costs is potentially worth it if you can guarantee the income for a period of time. It’s the same reason why regular savings accounts have higher interests than a standard account.

Idk about ultimate guitar, but on songsterr there is already a button to do that. If you first press the latest revision date:

It’ll bring up the revision history, each version having a download link.

It’s useful to have revisions in case someone changes the fingering somewhere and you prefer the older version.