These senior devs often quit or are fired and leave the rest of the developers with their “good ideas”.
I have never seen a junior taking on something new that is inherently huge and complex. I have seen them go overboard with refactoring, because someone tricked them into thinking the Boy Scout rule is good, or that DRY is important, or that they need to think ahead and abstract/generalize for the future. Inevitably that is something they were “taught” by senior colleagues or teachers.
A corollary to this is the pandemic of phobia for NIH. A lot of developers really seem to prefer janky, undermaintained third party libraries with huge APIs over a quick home made hack to solve exactly the problem your team has, and you can maintain and test and just know everything there is to know about. Building your own stuff is good. It is the business we are in.