I want to assume you are a recreational or amateur musician. Correct me if I am wrong.
U2 have always mentioned in all interviews that music is their job. Bono thanks Mullen Jnr for "the only job we've ever had" or when they had a good album they said they were "re-applying for the best-band-in-the-world job." A job needs pay.
U2 don't do think out of thin air just for the sake of making music. It has to make money for them because they don't know any other job or source of income.
From the band's point of view, they might have found better ways to cash-in on the current music landscape opposed to just recording an album. With U2's admittedly crude method of coming up with new albums and recording studio jamming-without-a-plan style, it will be very expensive for them.
If the band remaster their old catalogues, sell riffs to TV shows and even to mainstream top-40 singles-only artists, they might stand to make more profit and still keep jobs for their studio people (or their support system who depend on them for salaries) to remaster, rework, or remix old material. It would be less taxing and the wages would be the same.
From my fanboy's perspective, of course I want new material. I probably memorize all of U2's songs (except POP) by heart and want something new. In an ideal world, U2 will continue for the love of music regardless of losses and disappearing listeners. But this is not an ideal world, this is a "job" and "career" for U2, and they need to check their productivity, age, and profitability.
So what is the point in making a new album?
Nope, not a recreational or amateur musician.
I'm working toward pursuing it professionally/seriously and hopefully landing a record deal at some point.....not before touring and paying my dues, of course. The difference between myself and many pro musicians is that I do have a back-up plan as I have a college degree and a full-time job....but every hour that I'm not working I'm writing songs/playing my instruments. So I guess you could say money is kind of a factor for me, but not a huge one. I'd gladly do music full-time if it paid my bills and that's ultimately the goal.
The only problem with what you've written is that, while it applies to 99% of artists out there, it does not apply to U2. We know that Edge and Bono both have a significant amount of money from investments/endorsements--or at least they should considering some of the great investments they've made lately (Facebook). I don't know about Adam and Larry, but I'd assume as equal members of U2, they're netting a significant amount of money from royalties/tours/new albums. Perhaps 10-15 years ago you could say money was a concern for U2, but today, with a catalog of 30 years worth of songs and millions of songs/albums sold every year from said catalog, the guys are probably doing pretty well for themselves financially.
They can still sell/license songs while also continuing to tour/record new songs, if money is really a concern for them.
If they do not enjoy playing music anymore, then hanging it up makes sense. They don't need to keep recording new music to stay afloat/rich.
If they DO still get a thrill out of playing/recording music, then making a new record (or several) makes sense. Most musicians, unless it's truly a "job" or something they're only doing for the sake of being famous/making money, get a thrill out of creating new music. That's why so many struggling musicians continue to make music--because of the thrill and creative fulfillment. Even if my music never takes off, I'm always going to pick up a guitar or bass or write lyrics simply because of the enjoyment I get from making music. I'd like to think U2 have the same passion for music, and if they don't, it's probably time to go out.
Thing is, with how poorly the band seems to have viewed NLOTH, I can't imagine them going away now. I would think they'd be more inclined to try to make one or two more great albums before going away, just to ensure that their legacy stays in tact. And they're still relatively young, so even if they do hang things up, it wouldn't shock me to see them come back together in 10-20 years time. I mean, look at the Rolling Stones. They seem to take significant breaks between touring and then come back together every now and then. Same could happen with U2.