I would say a big contributor is also reference semantics for classes being the default behaviour in many languages. You end up sharing the state and increasing the surface area of your code which can touch the state with every pass-by-reference in the code base

I know there are mechanisms to avoid this, but many times they are opt-in rather than opt-out, and so it encourages this access-to-state propagation through the codebase where you have far reaching consequences