The new restrictions had to be put in place because users kept creating new accounts to evade bans given by cheating and hacking into games.
For starters, you can no longer store games equipped with Valve’s Anti-Cheat System (VAC). Before you could store it in your inventory, but now you have to immediately play or gift a title after it is purchased.
The VAC is used in a handful of multiplayer games like CS:GO, and results in bans if players are caught breaking rules.
You also can’t gift games to other banned users, else you won’t be able to gift that particular game again, even if you unknowingly sent it to them.
Here’s what Valve has to say about it:
“When a user is caught cheating, their Steam account is banned from playing multi-player on secured servers,” the support team wrote in a post about the gifting limitations. “This creates an incentive for people who cheat to stockpile copies of games on one account and to gift them to low-value accounts where they can continue cheating. In response to this problem, Steam no longer allows users to purchase copies of VAC or Game Ban enabled games to their inventory.”
The full list of restrictions can be read here.