Thanks for chiming in...
As far as I can tell this is due to KM attempting to parse the macro master list. I have roughly 360 macros I've built, most of which use some kind of image recognition. These aren't light macros per se, and I get that... However if KM's editor weren't written in such a way where every single macro is tangled up with every other macro this wouldn't be an issue.
Macros that were heavy on their own would be more resource hungry, this is something I deal with day to day in Logic. Some projects require you to scale things back by temporarily rendering things to audio. KM Editor's approach however would be equivalent to me being required to open every other Logic project and temporarily rendering everything to audio before I could resume working on the current project. I'd wind up spending more time trying to stabilize Logic than actually creating something with it...
I've found my master macro list, the single plist is 200 MB. Just attempting to preview the plist causes finder to pause for about 3-5 seconds before it can display it. Because KM lumps all macros into a single file the editor is having a hard time parsing any one macro because it's attempting to parse an insanely large file that even finder has a difficult time displaying.
This approach of wrapping everything up as one massive file would be like Premiere, Davinci, or an equivalent video editor storing each discrete project inside one single master file; and the ability to edit each discrete project hinged on the sum total of events inside that master file. The moment you had a project where scrubbing the timeline became an issue, scrubbing the timeline in every other project would also become an issue. Essentially it'd be the equivalent of that application requiring you to work on all projects at the same time.
The same could be said about any other application... Imagine if every time you edited or created a unique image photoshop's overall performance started to degrade.
As far as the (apparently intentional?) limits (<1000 macros, <20 actions, etc)... Sure, you probably wouldn't want to write a novel using notes. However notes doesn't limit you to the number of notes or characters you can write, and the user is free to write as little or as much in it as they'd like. Frankly this is like saying that an email client whose inbox can't handle more than 1000 emails, and whose replies cannot contain more than 20 unique words would be a well designed email client.
This is the developer's choice and I respect that, that said, I hit its ceiling in only a month. I personally find this to be an incredibly inefficient way to design an editor.