It's possible the codebase was a patchwork of Bootstrap, PHP, Wordpress, and jQuery UI plugins that could buckle under a production load. It could have been a good idea poorly executed; we just don't know right now.
So like most enterprisey software. You'd be amazed how much enterprise software has a customer of 1 and any bugs the end users have a workaround simply because they are a captive audience that had this steaming pile foisted on them.
There's a good chance the app did what it was supposed to just fine, but Delta couldn't sign on because it didn't have Reporting Requirements, SOC2 Compliant or a litany of other things that an Enterprise would require to sign on.
I work for a company that sells a SaaS product, it's not unlike many others, but we win sales based on how flexible / well we integrate with our customer's wonky systems.
What our application does is roughly the same as anyone else's ... but for many customers ease of integration with their systems is the make or break point.