Do you know why this border info of Excel sheet make it's size lar
 

Hi,
One of my coworkers asked me to shrink a file size of Large excel file.
It has only one worksheet and also few contents but it sizes over 11MB !!
When I scrolled it down, I feel a delay but there's nothing special to
consume a resource on it.
I looked for other options objects, any unkown link, voices which can make
it large, but there's nothing of them.
I tried to remove all contents first.
Secondly, when I tried to remove a border (table) on it, I met an Excel hang.
Those borders donot seem to move/copy other workseet.
I wasnot able to remove borders so I copied all then pasted them on new
Excel sheet without border.
Then new Excel sheet turns normal size now.

I have no idea why this border info make this Excel file so big.
Would somebody let me know how to fix it not like this ?