Some religions believe that eating meat in some important day are incorrect
Catholic doesn't eat meat every Friday.
Somebody don't eat meat because eating meat is cause to increase of killing animal. In buddhism must not kill animal in the buddhist holy day because it is a sin and this day have to make good things.
บางคนไม่กินเนื้อสัตว์เพราะว่าการกินเนื้อสัตว์เป็นต้นเหตุของการฆ่าสัตว์เพิ่มขึ้น