Most Helpful Girl
Because they were from two different worlds.
Her parents represent an uneducated world without imagination. They accept what is fed to them (on TV).
Matilda, on the other hand, disregards "societal" (her family's) expectations and standards and finds her own path and escape via books.
Most Helpful Guy
I think they were miserable who couldn't handle their daughter being different. They started to see her succeed and were jealous so they mistreated her to sabotage her.
One of the favorite Movies by the way.