It looks like BGS made back Starfield's rumored $200 million budget on Steam alone in 2023. Larian rolling in it though!!!

Still haven't purchased the game yet. 

True, although I believe Valve pockets around 30% of that.

Don't know where this image is from or where they claim to have got these numbers but this isn't the top 10 games by revenue. Valve released the highest revenue steam games of 2023 themselves. Didn't reveal the revenue or the exact ranking order but they are grouped as:

Platinum: 1st - 12th
Gold: 13th - 24th
Silver: 25th - 50th
Bronze: 51st - 100th

Cities Skylines II is in the silver group, so it was ranked 25th or lower as of December 15th 2023.

Best of Steam - 2023 (steampowered.com)

Good point lol. Although it'll be 20% in this case since the game crossed the $50 million in sales threshold. 

These are for new games that released in 2023, not the general categorization placement you're mentioning, which is mostly comprised of years old titles. 

Although I am trying to find out the source though. I'm seeing this info get passed around on reddit, twitter, youtube, etc

That makes more sense then. I'm guessing they got sales estimates from a site like playtacker, vginsights etc and used that to estimate revenue. Not very accurate but the best you can do without official information.

Source is: Video Game Insights - Games Industry Data and Analysis