NBA Basket Ball

I tried again last night to watch the finals. I would have to say I like the Celtics for some obscure reason.
Every game I seen includes the chant - boom boom Defense! Then there are some guys that dribble around a bit and when there is seconds left in the shot clock the either pass it to some shcmo or try a long range shot.
Why didn't they try that 20 seconds ago. Especially when it is in the last quarter and time is of the essence.
And why don't these strechies know what is a foul and what is not? I'll admit I have no idea what the fouls are about, but these guys have played the game for at least several years and should know what to do and not do.
I can't understand why the don't immediately try a 3 point shot or a alley oop; it save time and it just as high a percentage play as the typical dribble around the court until panic sets in.