Gambling counter

The gambling counter in the lower right of the vendor window. It wasn't clear the me initially that I had to kill unique mobs to increase the amount of items I could gamble. Whys is this a even a thing? If we have the gold we should be able to gamble items as much as we want. Also, are the gambled items based on our item level or the level of the zone that the vendor is in? I assume it is the former but this isn't made clear.

nevermind i see the small counter in the lower right corner, took me asking Sirgog on twitch to find it >.<