Why Don't We Finish More Games?

IGN has an opinion piece discussing why, as video games get shorter, we seem less likely to finish them than in the past. For example, BioWare said only 50% of Mass Effect 2 players finished the campaign. The article goes into several reasons gamers are likely to drop games without beating them, such as lowered expectations, show-stopping bugs, and the ease with which we can find another game if this one doesn't suit us. Quoting:
"... now that gamers have come to expect the annualized franchise, does that limit the impetus to jump on the train knowing another one will pull up to the station soon enough? ... In the past, once you bought a game, it was pretty much yours unless you gave it to somebody else or your family held a garage sale. The systemic rise of the used games market now offers you an escape route if a game just isn't your bag. Is the middle of a game testing your patience? Then why not sell it back to your local game shop, get money back in your pocket, or trade it in for a game that's better – or at least better suited for your tastes? After all, the sooner you ditch it either at a shop or on an online auction site, the more value you stand to get in return.