Channa is absolutely right.

In reality, CO is giving out funny money (sort of like miles but a bit more useful). So next time ma and pa schmo are traveling, they might take CO, even if the ticket is significantly more expensive because they *have* to burn the voucher. But they will still remember how generous CO was with bump compensation and perhaps, if they're into that sort of thing , book more with CO in the future. And if they don't take any trips, oh well, that's a liability that disappears.

Giving some nobody customer an upgrade on a flight that's say A2 while there might be H fare plats on the flight in Y is a bad move. "Even on an H fare I can't get upgraded on SFO-IAH!?". The nobody goes "oooh this is sooo naaahce" but would never shell out for it. That's a bad move.

CO has a well-deserved reputation for lowballing VDBs. For all the hoopla about maintaining the integrity of the premium cabins, another $100 is nothing.