How could they miss it if the only way they can choose it if Fiverr offers it to them? There is no other way. They can’t miss it because it is part of the checkout process.
You’re assuming people don’t choose it because they don’t know. But that doesn’t make sense…the only way they get the option is because Fiverr notifies them.
And in your suggested offer you aren’t notifying them, you’re asking them to do it for you. That’s coercion.
Your point doesn’t make sense and it’s just an excuse to coerce buyers.
Instead of trying to find a way to coerce buyers, create work that people want to share.