I think ERPs are a basket case category generally. I've worked with SAP for a few years (or more accurately work hard to keep it out of scope for what I do) in my day job. I've also worked for a company providing ERP stuff for SMEs (mostly S).
Anyway SAP/ERPs aren't code for running your business. They're code for running code to run your business. Now you have all the shortcuts SAP made to get stuff out the door, and on top of that you've got all the layers of shortcuts your business has made to get things out the door too. Therefore lots of nasty difficult complexity.
And finally I've seen evidence that in SAP people treat it like the fundamental abstraction layer is the spreadsheet[1]. So like in unix everything is a file, in SAP everything is a spreadsheet. This is a nasty complicated fundamental abstraction without the natural elegance of Unix's one.
[1] Maybe it really is, maybe it isn't but that's how a large chunk of the ABAP code I've seen treats it.
Anyway SAP/ERPs aren't code for running your business. They're code for running code to run your business. Now you have all the shortcuts SAP made to get stuff out the door, and on top of that you've got all the layers of shortcuts your business has made to get things out the door too. Therefore lots of nasty difficult complexity.
And finally I've seen evidence that in SAP people treat it like the fundamental abstraction layer is the spreadsheet[1]. So like in unix everything is a file, in SAP everything is a spreadsheet. This is a nasty complicated fundamental abstraction without the natural elegance of Unix's one.
[1] Maybe it really is, maybe it isn't but that's how a large chunk of the ABAP code I've seen treats it.