Continuity mistake: Lady Tanaka's daughter's earrings are removed during her fight with the Punisher, but they're back on her ears after she's sliced his arms with them then they're gone again. (01:40:16 - 01:44:46)
Continuity mistake: In an earlier scene when The Punisher is at the mobster's house and the house gets set on fire, he is standing in the doorway killing bad guys. One second he is in the doorway and the next he is standing firmly on the ground.
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.