I have no idea and I don't work on that bit but there are lots of troubleshooting guides on "what to do if Defender is slow in situation X" in our docs - in 99% of cases it's interference (another program scanning) or specific programs acting in ways that trigger scanning often.

In all cases there are workarounds - I'm not using the Windows version (I'm on a mac) but when I had a performance issue it ended up being a script that created and deleted thousands of files quickly and tweaking it was fairly simple.