Oracle doesn't sell to you. Oracle sells to your vice-president, on the golf course. The reason they have this free-tier at all is to be able to say "yes, your engineers can go in and evaluate this for free".
Can’t a CTO say « no »?
Maybe the Oracle of old, but this strategy isn't common for any cloud vendors these days.
Same way that lawn mowers convince people to stick their hands into the blades, despite common sense and all the warning stickers screaming at you to not do that. It seems expedient in the moment, you're not thinking about long term consequences and just want to fix a problem fast right now.
Because it integrated with OracleDB.
But if you are still stuck with OracleDB, you are probably not happy about that and you can get it in other clouds providers anyway.
If someone is "stuck with OracleDB" then it sounds like they don't make the purchasing decisions.