Greets,
Well SghnDubh covered the why pretty damned well, so all I'm gonna do is give you another example of the same logic in a different package.
When you first started running missions to get cash, or standings, etc how did you do them? Would you lock the max amount of targets you could and then split your damage among all of them, or did you put all your damage on 1 target at a time?
I dunno why, but when alot of people start out missioning they tend to split their damage among all targets. Then they learn that they will survive alot longer if they simply reduce the # of ships firing at them as fast as possible. Splitting your damage among multiple targets only works if you can 1 or 2 shot the targets. Anything more, and you are better off focusing your fire on 1 ship at a time. This is ofcourse from a PvE standpoint, but from the number of times I have heard a PvP'er say "primary target" it makes me think it carries over to PvP to some degree.
Do you see where I am going with this? It does you no good to have 500 dps if you only put 50 of it at a time on a ship. By mixing your ranges, you are doing just that. You allow your targets to survive longer, you take more damage, and you prolong the fight. In PvE the length of the fight has little bearing. But in PvP, the longer the fight, the more time your target has to get support to his location.