When I first started my career we were selling PCs into a market where two programs were major roadblocks to windows 3.0 upsells: Lotus 1-2-3 and WordPerfect. If you were a legal secretary WordPerfect was near irreplaceable in a market where the user had transitioned from a typewriter only 5 years ago. Non technical users who has mastered mail merge in WordPerfect would rather beat you up and leave you in the gutter…
The only other comparable stack of the era, maybe slightly later, would be MS Access. When you’d get a call from a prospective client who’d explain they had a member of staff leave and now nobody knows how the Access database works.
“Accidentally load bearing” is an apt term