Large projects in OO often end up as mutable monoliths which become harder and harder to work with. New features sometimes require large painful and scary changes. Hacks are irresistible. Of course you need refactoring tools because you have to change many things in many files.

OO promised modularity but the languages never delivered because of their unreasonable design.

Highly reasonable, concise and refactorable code is the answer to complex systems.