Jon_Irenicus_PL: Steam does refunds way faster than GOG, and they are automated.
Because they have DRM and DRM enables automated refunds (you lose access to the game). With GoG, you could have downloaded the installer and still have access to the game after you refund.
GeraltOfRivia_PL: So i can't refund if i simply dislike the game?
You can, but you shouldn't, as this is what is commonly known as a "dick move".
Per the policy, which you can read for yourself:
"How often can I refund my games? Is there some sort of limit?
We trust that you're making informed purchasing decisions and will use this updated voluntary Refund Policy only if something doesn't work as you expected.
We reserve the right to refuse refunds, or only offer Wallet Funds conversions, in individual cases.
Please respect all the time and hard work put into making the games you play and remember that refunds are not reviews. If you finished the game and didn't like it, please consider sharing your opinion instead. Also, please don't take advantage of our trust by asking for an unreasonable amount of games to be refunded. Don't be that person. No one likes that person."
As for your other question.... You really do know why.