Simple answer
> When my count is very negative, I just play basic strategy
> and enjoy the 5 min break for my head...
If you need to take a break, get up and leave for a few minutes...you won't miss anything.
You ask us why we leave a table in a negative count, but I ask you why you wouldn't? We are advantage players. Why would you purposely play when you don't have the advantage?
The count will be negative more than half the time. If you flat bet $5 each hand and play basic strategy for 50 hands per hour you are giving away over $1.50 each hour. That may not sound like much, but if your boss offered you a $1.5/hour raise for doing less work wouldn't you take it? If you want to throw away a few bucks every hour, you're better off tipping the dealer. At least they will get your money instead of the casino!
Also, by leaving in negative situations you will lower your variance quite a bit. This can be VERY helpful in shoe games where your big bets will cause much bigger swings in your bankroll.
Another benefit is the potential for higher win rates. If you are always looking for better counts when the shoe goes bad, you are more likely to find more positive situations.
Sure, it can look very conspicuous to be switching tables after only a few hands, but there are several ways to make this type of strategy work for you. It is definately worth the effort.
-Sonny-