Why do we still get gmail invites

Back in the day it was necessary to beg the lucky few who actually had a Gmail account, to send you an invite, in turn you dished these out. The reason for this was to keep the load on Google's servers to a manageable level.
You started out with a few invites which, as Google's capacity increased, also increased. eventually I ended up with 100 or so. I have dished out 15 as can bee seen in the screenshot below.

Why is Google still displaying this facility to invite other people to Gmail, when you can simply go to www.gmail.com and sign up for one by clicking on a link on the homepage?

Come on Google. I know we can minimise it so that it is barely noticeable but it's still there. At least give us an option to hide it completely.