Why are champions getting harder to unlock?

We know that unlocking champions doesn't really make riot any money, as they've said so themselves. Then why are they continuing to nerf ways for new players to acquire them? I somewhat get nerfing free skins (obviously not to this extent but that's not what this post is about) at least from a business standpoint, but making it take years to unlock the whole roster just seems extremely discouraging for new players. I know they said they're buffing blue essence rates in the new BP, but that still doesn't really seem like enough. The argument that riot has historically used to defend having to buy champs is that 170+ champs would be overwhelming for new players. While I think this is a reasonable argument they definitely overshot in the other direction.

TL/DR: why not just make all champs available past lvl 30 or something?