I'm sure the intentions are good. Rewarding desired behaviours reinforces the behaviour. Of course it also reinforces the rewards.
Teachers teaching their students, usually their very young students, that candy and pizza are rewards for every job well done no matter how small, might not be a great lesson for kids.
Moreover, there are so many better rewards that could be metered out.
In no particular order, here are ten (some whole class, some single kid), and please feel free to share this post and list with the your children's teachers. Honestly, they care about your kids, but they may not have thought about the issue much, and they're just doing what's nowadays considered to be normal.
1. An extra period of recess
2. An in class dance party
3. Dress up (or down) days (PJs, costumes, fancy clothes, whatever)
4. Class put in charge of school PA system for the day
5. Painting a hallway or classroom mural
6. Stickers or temporary tattoos
7. Sit wherever you want for a period (teacher's chair, floor, under desk)
8. Get out of one night of homework free card
9. Phone a kid's parents to tell them how terrific their kid is
10. Scrabble/boggle/other sort of educational game competition/hour