Buffet restaurants don't encourage you to over-eat. That is the choice of the person who forces himself to eat as much as he can, to "beat the system". It is preposterous to blame the buffet system for this.
Further, in Islam, we are encouraged to share and eat from one plate, sort of like a large buffet as per below. It doesn't mean that you should eat the most, but rather you eat what you wish according to the principles of Islam (1/3 of the stomach for food, 1/3 for drink, 1/3 for air/empty):
Al-Wahshiyyi ibn Harb radiallaahu ‘anhu related that some of the
Companions of Allaah’s Messenger sallallaahu ‘alayhi wa sallam said:
O Messenger of Allaah! We eat, but do not become satisfied.
So he said to them: “Perhaps you eat separately?”
So they replied: Yes.
So he said: “Eat your food collectively, mention the Name of Allaah
upon it, then there will be blessings for you in it.”
Shaykh Ibn al-‘Uthaymeen said:
“This indicates that it is essential to eat collectively from a single
plate. So if there are five or ten people, they should eat
collectively from a single dish, depending upon the situation. Indeed,
doing so is a cause for barakah (blessings) to descend, whilst eating
separately is a cause for barakah to depart.”
 Hasan: Related by Abu Daawood (no.3764). It was authenticated by
al-Haafidh al-‘lraaqee in his Takhreejul-lhyaa (214).  Sharh
Riyaadhus-Saaliheen (7/231) of Ibn al-‘Uthaymeen.
Source for the above: Al-Istiqaamah Newsletter, Shawwaal 1418H /
February 1998 ,Issue No.8
Above is from https://abdurrahman.org/2011/06/07/eating-collectively-from-a-single-plate/