Chessed or service. Call it what you want. Whatever it is, it cost them money to run. The shadchanim work there for free and should be paid by the couple upon a successful shiduch just like any other shadchan.
The mitzius is that people won’t pay for something if they can get it for free, hence the restrictions on free accounts, it is just a trial, if you like it, sign up for the paid version.
Think of it as a singles weekend where you have to pay, you are paying to cover the cost of the event, not the shadchanim.
It happens to be a great service and I think it would be great for the “shidduch crisis” if ALL singles signed up so that the shadchanim on the site can have more of a choice to choose from. (We’ll leave it to AZ to tell us at what age each gender should join).