Everyone start with 3 slots for giveaways. And for every 3 giveaways confirmed as received you get one more slot, but deleted giveaways or confirmed as not received take away a slot. Of course, if you need more slots, you can create a support ticket requesting the amount you need and wait a little to get them.

It's made to prevent new users from creating many fake GAs. Imagine having 100s or even 1000s fake GAs...
With limitation it can be only 3 of them - then usually user is suspended and doesn't have free slots.
If he wants to make real giveaway, he will have to send support ticket, so he will be asked what game is it (that he wants to give) and how he obtained it.

Optionally for bigger trains you could also ask for increasing limit.

Any continuation? :)