Why does it have to be monetary value?
Why do you assume that most kollel men are doing what you call “serious learning”?
I think many are in kollel for just a year or two. They feel it’s important to start marriage that way to set the tone for a home where Torah is central, but aren’t in it long term. These are the ones who are often (not always) less dedicated and learn fewer hours.
The other thread (http://www.theyeshivaworld.com/coffeeroom/topic/being-in-kollel-but-not-a-ben-torah) is probably the place to discuss whether this is worthwhile. I think it is.