The issue is that of network effects. Making it harder to sideload for example f-droid makes the already small market for it even smaller, leading to less apps. It also forces people developing Apps that they don't want to reveal to be developing for completly valid reasons (Imagine developing a porn app in saudi arabia or an abortion support app in the USA) to validate against google aka the US Government.

I'm just presenting my exotic point of view - since that developer verification would only be needed to run apps on the "stock OS" (which I consider bad), then deliberately excluding it could promote using LineageOS/GrapheneOS which would be a good thing.

But of course I'm talking about non-commercial apps, but commercial app developers would already be on Google Play.