Also because Romanized Japanese is completely unreadable from the sheer amount of homophones. You cannot tell by reading the term "hayai" whether I mean 早い or 速い, which mean different things. "koto" can refer to "stuff" or a stringed instrument. "sentaku" can mean laundry or a choice. Romaji is completely useless except for maybe karaoke. Even Japanese learners are told to NEVER use Romaji.