I have often wondered the same thing. I appreciate a parent organizing putting together gifts for the teacher, so no, I don't get upset. I was a room parent last year and sent out an email letting parents know I was collectiong money for the teacher's (Christmas/end of the year) gift. They could donate any amount they wished. Some donated $3 and some donated $25. If they chose to particiapte, they could, but they were not obligated, of course. I would say that half participated. On the card, I added the names of the children who participated, but not the amount they contributed. Some parents may prefer to give their own gift, so that the teacher knows what exactly they gave, and some parents, I'm sorry, may just be cheap.
BTW, my co-room parent didn't agree with just putting the names of the children who partcipated but thought I should add all the students' names to the card, even the ones who did not participate. I did not agree.
I've collected money for gifts for my daughter's teachers for the past several years, and yes, the gifts have always been monetary. No offense to anyone, but teachers get so many of the same usual gifts that I would just rather be very very practical.