The kind soul turned LandLord

An ant knocks the door of a HDB flat.
House owner opens the door.

"I want a place to stay", said the ant .
"I have a vacant room which you can occupy for free of cost", said the owner.

Ant went inside and occupied that vacant room.
After some days, the ant brought in another ant and requested the owner:
"Can you please allow this ant to stay along with me".
"Oh sure, you can do so without paying any rent" said the owner.

After some days the ant brought one more ant and requested the owner to allow that ant to stay with it. Owner agreed to it without asking for any rent.
This continued i.e ant brings in one more ant and owner agrees for it.

On one fine day, the ant brought in tenth ant and requested the owner to allow that tenth ant also to stay with it. The owner said "Ok, you all can stay here but you need to pay rent".
Now the question is Why did the owner ask for rent when the tenth ant came in?
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Scroll down for the answer
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GUESS FIRST.......DUN PLAY TRICK........ Please help me, give me some guesses 1st :)