Because they have very stringent qualifying requirements.
When I first signed up with them I had a lousy $200 weekly limit.
Got it bumped to $500 but got tired of dealing with them.
For example, when I moved, Ichanged email address, they wanted an explanation, same thing when I wanted to use a different bank account, they wanted a reason before they'd update the account info.
What annoyed me the most with them was if I got a $USD payout from a poker site into my Instadebit account and wanted to send a $CAD deposit to Pinnacle they wouldn't convert the currency, they required me to withdraw the US to my bank then they would withdraw the $CAD from my bank account. Plus the week to 10 day waitng period before you could withdraw once you made a deposit via instadebit.
I converted everything over to moneybookers and no longer use instadebit.
Instadebit a real pain in the ass!
Moneybookers is much more convenient for moving money around.
Actually, with Pinnacle they are very good, why? Because Pinny will let you deposit via credit card or bank draft and withdraw via Instadebit, that is convenient.