Isn't the entire point of having a throne "pushing your limits"?
I'll take Siege Engine by Buckethead as an example. I played that song a while ago, and scored 218k on it. This other guy, Blazted, took his throne back.
Now, a lot of months later, we're already at 805k. Isn't that beautiful? At first, 800k seemed to be impossible to reach - it's almost 4 times the first throne. Now is even 1 million coming within reach, and we're planning on racing on 'till we get there.
Imagine Blazted and I were allowed to play the song only 20 times. Let's say it takes about 5 or 6 tries average to take the throne back, improving it by 30 to 50k, sometimes even less. To make things easy: 5 times per person, improving the score by 50k. That would make 5*2 * 50k = 500k added to the original throne. That would have killed the song at 718k, which is funny enough the score I held the throne with for 9 weeks due to holidays

. But do you see what's happening? The race would already have died, while it is now still going on. It's not like we play it excessively, but we just keep on playing it on a steady base.
With your idea, the scoreboards of the entire game would be killed in about 3 months.