Games removed from Steam

I just noticed that a large batch of games were removed from Steam today and no longer eligible for booster packs if you already own them. Most or all look like ones that had been given away for free as far as I can tell. Anyone know what happened to cause their removal?

Here are the ones that affected me:

• The Note
• Pixel Space
• Weapons Genius
• Cosmic Rocket Defender
• Invasion
• Quick Slick Deadly
• Shut Up And Dig
• Princess.Loot.Pixel.Again
• Wishmaster
• Unknown Battle
• BitRay
• PixBit
• EeOneGuy Adventure
• Yellow: The Yellow Artifact
• JDM Tuner Racing
• BoneBone: Rise of the Deathlord
• Numberline

edit: GraVe23 helpfully provided a link to an ongoing discussion about this:
https://www.steamgifts.com/discussion/tZOVf/psa-steam-doing-small-purge-aka-new-ban-wave-on-the-store/search?page=6#sf6IMhJ