It’s no wonder he ended up doing what he did. Victor Frankenstein was more of a monster than the creature he created. As the book ends, father and creature sink to the depths in polar water and assumed the end of them both.
Other books have tried to expand on the Frankenstein mythos and movies have tended to treat him less than a tortured soul and more of the monster. It’s a classic case of people fearing what they don’t know. Had Frankenstein accepted the creature and spent time helping him learn and letting the world see him for what he was.
Instead, Frankenstein treated the creature like property. It was an experiment that needed to be hid away even though it longed to be outside. It had no social skills and no way to deal with the unknown forces of the outside world.
The operations used to create him, left the creature hideous and corpse-like. He was treated like a dog by Frankenstein and it’s not surprising he escaped. The people who saw him thought he was a monster and he changed his behavior to suit. Had things been treated differently, Frankenstein could have had a very different ending.