The author says "Toto was not the sort of pet we could keep for long" because Toto was very mischievous and caused considerable trouble. Toto constantly disturbed other animals, broke dishes, tore clothes, curtains, and wallpaper, and was difficult to handle. The family could not afford the frequent loss and damage caused by Toto, which made it unsustainable to keep him for a long time. He was not friendly with other pets and was disruptive in the household, leading to the decision to give him away or sell him eventually.
