Thats because it Eventually Mallocs All Computer Storage.

Escape-meta-alt-ctrl-shift!

I'm often surprised how Emacs can struggle sometimes on modern hardware, like for example when chain-executing complex keyboard macros - though mostly yeah, it doesn't apply all that much anymore.

Emacs is actually faster than most editors, but it lets you do anything so of course you can slow it down.

The issue is it remains non-concurrent and any code (macros, extensions, …) executes in place of the editor doing its thang, so any non-trivial operation (or trivial operation on an entire buffer) locks up the editor until it's done and does its thing.

And while it might technically be faster for the process, as is the case with e.g. STW GCs on large processes it 1. feels horrible and 2. as an editor is interactive it stops the user in their tracks and slows them down to hell