Some people disable chat because they don't want the distraction. Some do it to avoid abusive players.
Generally speaking, if it is disabled when the game starts it is configured to automatically disabled in their settings. It isn't a statement about you specifically.
Serious question here : why do people disable chat during blitz games? I find it rude, I go to type in "good luck" and the message comes up "your opponent has disabled chat".
This immediately makes me think : "well screw you too buddy!" and I kinda lose the desire to even play.
I can see someone doing it if It is interfering or I am chatting constantly through the game. But to start off with chat disabled? why bother?
So much for saying good game at the end.