I've seen similar inside large financial orgs - what struck me was how there are these huge amounts of people that spend their entire working life inside this alternate IT reality. It's not unlike SAP consultants where their skillset is tied to one company.
Also...these things tend to have fuckin terrible documentation. Good luck figuring any of this out. And you can't google it and your AI is just as lost as you
lolol. Actually, I find AI has a reasonable chance to figure it out, as long as you point to the right source code. BTW to me these quirks actually can be used as some kind of job security. If it takes a year to onboard someone to do meaningful work, it sure raise the cost of firing.