Because creating a currency without inflation was the main purpose. Without a transparent ledger, how can you audit the supply efficiently? You can fork bitcoin if you want and make it all private but no guarantees people will use it. Monero admits this tradeoff. 
Discussion
I also believe that the fixed/auditable supply is what matters first and foremost, everything else follows
Agreed. Most important 🤙🏼
Considering we have mastered that portion of the project, let’s focus on all the steps we can to accelerate privacy and managing fees.
I agree simple auditable supply over everything. Even at the expense of users much more easily being discovered and thrown in cages/censored.
I think the majority of people rely on the Bitcoin node software to do the calculation of how many bitcoins are in existence. I think most people rely on the math and don't try to verify the supply themselves. And if they are relying on the math to be correct for Bitcoin, then they can rely on the math to be correct for Monero. Monero has asymptotically zero inflation in order to keep fees low and yet still manage to keep the monetary supply under control because coins will be lost over time and it will hit an equilibrium.