I don’t think Monzo have set out to help you “make more money” per se, but rather put you in greater control of the money you already have and helping you save money (with the help of Marketplace). I believe Monzo feel that saving you money and putting you in greater control of your money is “the incentive”.
Tom (Monzo CEO) posted this on the forum mid last year and that’s pretty much always been the consensus since I’ve know about Monzo.
…of course, things may change in the future as the company grows and matures.