Because they might just have a network problem and be able to reconnect. If the opponent is gone for a few minutes the game will automatically give you the win. Plus their clock will continue to run.
unable to claim a win

the ipad app does not give you win. i sat waiting for my opponent, one "vedwarde11" for 13 minutes- ran the clock down from 13 to 0 did my opponent, but the app did not give me a win.

Yes, but the painful part is I was sitting there for 13 minutes in a 15/10 game. I wish the iPad app would give me the win in a 5 minute no-activity timeout, for example.
When I play in live chess, if the opponent abandons, why is there no option to claim a win?