No need to go lie on the internet. You don't need to remove the glass to open the case, it's still two screws and a sealing gasket. Removing the glass is more like an industrial process to replace a broken glass backing but retaining the rest of the back cover.

After you remove the cover you still have to remove a few pieces of the top layer of components, as described in guides like this iPhone 13 Pro battery replacement one: https://www.ifixit.com/Guide/iPhone+13+Pro+Battery+Replaceme...

Now, say you tried a DIY repair and you broke the glass, that'd be a different case of suckage, but that doesn't really mean that suddenly batteries aren't replaceable. There could be a discussion around ease of replacement but there is ease of manufacture and sealing properties to consider as well.

That guide has 36 steps which include melting adhesive, using suction cups and using a pick to detach the display from the case.

On top of that there are a number of peripherals to remove before even getting to the battery. To me that seems extremely difficult.

Rewiring the wire-wrap backplane of a (in comparison) low-power computing system from 60 years ago with just a wire wrapping tool and wire with only 2 steps is 'extremely simple' if we were to use your measurement of tools, steps and material, yet I doubt anyone replacing their phone batteries could do that... It's all relative.

By remove you mean completely melt and destroy. There's no easy way to remove it without breaking the entire glass back, this is bonkers.