I can only speak from my past experiences with B2B. We had many B2B customers running ancient applications that would connect to us and transfer incredibly sensitive data. Getting them to update even a single application was not an option. The application may have been running for decades. The people that wrote it may be deceased or retired. Nobody knows what to do if it breaks so they dare not touch it, stare at it, taunt it or talk about it. It just works and nobody wants to create the crap-storm of creating something new that does not cover all the edge cases as a day of down-time could be millions or billions of dollars lost. Nobody want to be the one that caused that history making moment. Adding to this the application may be reaching out to dozens or hundreds of companies, government agencies, etc... and each organization expects it to work a specific way, yet there is no detailed architectural documents that would allow someone to flawlessly make a new application. Flawless is the key word. If a new thing is not flawless it will be immediately backed out and never spoken of again.