I think large systems get so large and complicated that they become very hard to reason about simply and think about. They become difficult to change their arch

I think large systems get so large and complicated that they become very hard to reason about simply and think about. They become difficult to change their architecture or tweak them. So developer velocity takes a hit and the system is so complicated that it's hard to change anything. LibreOffice, Mozilla Thunderbird are of such scale that it's difficult to change these applications how they work today.