You absolutely can, the DRM part of Steam is optional choice by the developer. It can just be a Game Downloader.

You can even sell codes in your own store, WITHOUT STEAM GETTING MONEY. That's incredibly generous.

I don't understand why you would expect them to give away their features for free. That's like expecting a a restaurant letting you use their cutlery and tables with your own food.

Finally, you have never and will never truly own a game. No, not even when they came as CDs. It was always just a limited license.