Opinion: They're losing badly in the Cloud Wars and need to scrape together some sort of customer base in any way they can, even if it means burning money.
Three times i've tried using OCI to move Oracles own products from on-prem to cloud. All three times they told me not to bother as it wasn't supported.
Seriously if Oracle can't figure out how to run RDBMS, Weblogic and Opera what hope have i got?
And if they've spent $billions building out huge capacity data centres, but only have a few customers, then they might have large amount of capacity sitting idle that costs them very little to put into the Always Free tier. It's free developer-mindshare-marketing anyway.