Actually, NBA Finals games starting at 9:00 ET goes back to the mid-80's (right after the dreaded tape delay era on CBS). However, Sunday games typically started at 3:30 ET until several years ago, when they too were moved to primetime.
I agree it does suck for us in the Eastern time zone, when games generally end around midnight. Heck, I still remember 1986 like it was yesterday when the Celtics defeated Houston on a Sunday afternoon at the old Garden to win the NBA Championship. That game started at 1:00 ET, and by the time it ended and celebration was covered it was around 4:00.............leaving almost 5 hours of daylight after CBS' coverage ended. That's unheard of in this day and age.