These Seniors might be good at duct taping, overengineering or have a "my way or the highway" mindset but aren't capable of finding and implementing a good solution given the constraints.
It probably boils down to factors like intelligence, creative problem solving, ability to focus, reading skills, knowledge retention and a healthy dose of humility.
I guess everyone can (and probably should) learn basic coding skills, but it doesn't mean everyone can become a great software engineer.