This is a fairly common approach to help promote the viral growth, you might have seen other tech companies doing something similar too. Monzo growing faster indirectly benefits you, as a user because it enables Monzo to secure more investment (as it’s doing right now & deliver features / products sooner.
You’re not the first person to question this though & Naji has mentioned that Monzo wants to move away from this approach at some point -
For now, if you’re not comfortable referring friends, to this bank with a crazy colour card, you should only have to wait a couple of weeks to receive your card anyway 