Actually since you guys are curious..
The reason is actually due to expansion.
I plan to expand all my buildings evenly (about 10000sqm plus sqm each) such that they will end around the same date. Then I will not log on for some time while waiting ( will have plenty of waiting time

)
However some buildings are too big for expansion. You cannot add 10000sqm to a 25000sqm building. The limit is 32767sqm.
If I only add 7767sqm, then that building will end its expansion early. To avoid unnecessary inconvenience, I do not want to specifically login and manage my account just for a few stores and joineries. So I have to downgrade its size slightly so that it can take the full 10000sqm expansion. Also it will look nice to have all my buildings almost the same size plus ending expansion at the same time
Actually I do have another alternative, which is to wait a few more weeks before expanding these larger buildings... which is what I will do if nobody wants to trade.
Strange that no one wants to take up my offer... This is a good way to 'instant expand' your buidlings. You can upgrade the size of your building without having to wait, you just need to spend the money.
Where the two most valued commodities are time and money...
With time you can almost always get money in kapilands, but using money to buy time... you can only do that sometimes..