I bet that it does not matter that they are garbage. They are so entrenched in their market segment by the basic business requirements and existing business relations that there is nothing to "disturb" without rewritting it feature by feature with help of very expensive subject matter experts. Its a kind of project that takes 5 to 10 years to create MVP (its mainly due to knowledge transfer not technology) and is rather high risk.
There is a reason SAP is so big and most of its software is not the best (Im underselling it a bit here ...)
There’s like… two? They’re both garbage from my experience both as a frequent flyer and as someone who’s hosted one of them professionally.