Trivia: This film was not called The Punisher in several of the countries it debuted in, with examples being in Romania it was called The Avenger, in Portugal it was called Silent Fury, Mexico called it Revenge is My Name, and in Serbia being titled The Executor.
Trivia: When Jake knocks out the guy with the pizza box, the moment of him reaching down to grab a slice of pizza for himself was actually improvised in the moment by the actor Louis Gossett Jr.
Trivia: When Frank Castle is in the jail cell, he has nightmares and flashbacks to his family before and during their execution at the hands of the mafia. In one of the shots, his daughters can be seen wearing Spider-Man pajamas when squirting water guns at him. This is a homage to the Punisher's very first appearance in 1979's comic, The Amazing Spider-Man #129, in spite of the director's desire to distance the movie from the comics as much as possible.
Trivia: When Frank Castle is being tortured and the lady asks him, "Who sent you?", the line he responds with is "Batman." This line was completely improvised by Dolph Lundgren himself.
Trivia: Director Mark Goldblatt wanted to make this movie as far removed from the comic as possible, mostly just using Frank Castle's back story and loss of his family as a way to make a gritty revenge action movie. Wanting to lean away from the aesthetics and lore of the Marvel universe for his film, he did not include Punisher's iconic skull logo on his shirt in this version of the character, believing his black spandex suit would not translate well to live action. Years later, Goldblatt has expressed regret for this decision, believing had he incorporated the Punisher skull into the character's costume and marketing, it would likely have sold many more tickets.
Trivia: This film got a theatrical release in 1989 in most countries except for Sweden, South Africa and the US. It wouldn't be until 1991 that it saw a VHS and laser disc release in the US for home video. Part of the reason why it didn't get a theatrical release in the US is due to Lundgren's film Red Scorpion being a box office flop, leading to producers not believing he could lead as an action star and draw in an audience.
Answer: With how many criminals Frank has killed, many of them would definitely want revenge. By hiding in the sewers, there's less chance of him or his hideout being discovered. If Frank lived anywhere above ground, his enemies would be able to find him more quickly and kill him.