I'm so glad you asked!
Buying on itch.io:
- Supports creators - our default cut is 10%, but they can pick any.
- Lets you play the games you buy, DRM-free, whether you want to use our desktop client or not.
Many platforms out there are fighting for the "best Steam key reseller" title, which often means "the cheapest", and some are famously known for not caring whether said keys were acquired legitimately or not.
(Keep in mind that key reselling is something Valve allows because having more players now means more revenue later. If/when it stops being economically viable for them, they'll have no reason to keep allowing that. Those platforms might have to rethink their model then.)