Can one of you tech savvy guys tell me why ICO's don't use services like Coinbase to accept funds for their ICO's?

I see in my account where I could add a shopping cart to my website to take payments in many different coins (the same way I would add a Paypal cart) and that takes about 5 minutes.  Why don't these guys just use one of these services and they could accept just about any coin?

Does it have to do with the audit process? (i.e. wallet numbers are not the same with a service?)

I am new at this so please go easy on me