Which seems rather short-sighted when instead he could do what he did for tens of thousands of years and just let the Mortals worship those who they felt were worth worshipping.
Honestly, it isn't like mortals are bad at devotion. We are really, really good at it. We have millions of people following cult leaders world wide, if literal Gods can't do better than a single charismatic man or woman, then they deserve to fade into nothing.
It's difficult to say to how us, human mortals from Earth, would act if placed in a D&D world.
On one hand, the gods there are provably real, on the other, they're flawed polytheistic gods, not perfect beings. They're often former mortals.
On one hand, great magic power can be obtained by serving the gods, on the other, it can also be obtained by studying the arcane arts, making eldritch pacts, or just by being charismatic performers. You can obtain demigod-level power without ever caring about the gods.
I do think that the setting makes enough sense as is. I think it's a believable fantasy setting.
Could the writers just say "screw it, from now on faithless mortals aren't punished, and that won't have far-reaching consequences because the faithless are going to be few and far between, anyway"? Sure, they could if they wanted to. At some point during 4e, the writers pretty much deleted more than half of the FR pantheon, because they felt like streamlining the setting was a good idea. They can do whatever they want.
My question is, would removing the wall make for a better setting? I'd argue that it wouldn't.
The wall of faithless is an element of lore that makes the Realms more interesting and unique. The setting would be lessened, not improved, by its removal. And really, why remove it? What do we gain by removing the wall? I know what we would lose: a fascinating piece of lore and a number of interesting plot hooks.