This seems to be very common in companies not paying attention to codebase, i have also worked with companies in past and they also had non maintainable codebase. And i was more surprised that the creator of the system was an engineer with 10 years + experience, but when i saw his coded apps (android and ios) and webservices / web apps, the code was mess (not easily describable in few words )
Their short answer to this is :
Page loads, content shows, user can use the site ? Yes ? , then its all fine codebase is not a priority and let's go ahead with adding new things in
In my experience i started to care less about existing code(just give focus on security and performance) and started focusing on my new coded files to be organised and easy to edit and easily extendable code, and not to do huge changes in existing codebase until asked to do so. We should do our best to make the future of that system better and when asked start changing things in old one.