No cause literally- if Toto was on a leash, Dorothy would have never ran away. She only runs away cause Toto kept going into Myra Gulch’s garden ti chase her cat, and Myra went after him so he bit her - which is why she gets a order to put him down.
Seeing Toto on a leash in the trailer is so funny because A. They had to put it on a leash because the dog is Ari’a pet and is not trained for film & B. 90% of Dorothy’s problems in the wizard of Oz is because she refused to put him on a leash.