The reason to distinguish the value of gifts is to curb the bad atmosphere of giving gifts on Teacher's Day. Gifts made by students themselves, such as handmade gifts or snacks, mainly lie in their value, but in their intention to the teacher. Giving these to teachers on Teacher's Day shows students' respect and love for their teachers. Then I think teachers can accept this relatively low-value gift from students.
But if these gifts are not sent by students themselves, but by parents through their children's hands, such as some flowers, skin care products, red envelopes and even luxury goods. Then the teacher really shouldn't accept these gifts with great value, but should instruct them to return them. This is because once this kind of thing is allowed to exist, teachers' day gift-giving will become a trend, affecting the quality of teachers' groups and causing confusion to students' parents.
Maybe at first, parents considered whether to send or not. After most parents gave them, some parents began to give gifts for fear that their children would be bullied at school if they didn't give them. When all parents start to give gifts, the follow-up will become comparing with each other, and each parent will give some gifts with higher value to the teacher. If this development continues, then Teacher's Day, a festival celebrating teachers' virtues, will be destroyed in essence.