To be fair, I wouldn't call DD's sales "good". In June, DD #507 sold 34,744 copies. The title's sales fell 10% other the last six months and 16% since June 2009. It is worth mentioning that DAREDEVIL #500 sold over 74,000 copies, yet a few issues later sales fell below when DAREDEVIL was still renumbered; #119 (before the old numbering returned) sold about 41k. Like virtually every comic book, DAREDEVIL was in a state of slow and steady decline, month in and month out. Books that remain steady are books whose debut was so high that it takes a while to hit the danger zone, or drops of 1%-3% a month. DD was slipping 4%-7% a month before July.
SHADOWLAND #1 sold just under 55k, which some are calling middling for an event (which Marvel denies is one). It was under-ordered and will see at least one reprint, if not two. But even if those reprints boost it's sales to, say, 60k for that debut, that is about where WAR OF KINGS #1 started off last year. However, DAREDEVIL #508 saw a sales boost from July, moving under 38.5k copies - or back to sales levels from December.
My point in all of this is that DAREDEVIL's sales are not steady and are not terribly high. Marvel would like to see it do better, especially the guy in charge who used to draw it. If not for the success of Quesada's MARVEL KNIGHTS line and his run alongside Kevin Smith, he would not be EIC. Before Joe Q decided to meddle with Spider-Man, the last comics he drew was a Daredevil mini, if memory serves. Obviously, Marvel was going to try something to revive the title's sales. SHADOWLAND is one step of that, and at least for one month it turned back the clock on DD's sales decline, at least to the glory that was 12/2009. It will remain to be seen whether those sales hold up.
Your overall point, though, is valid. It does make little sense to launch a big #500 issue and then cancel it barely a year or so later. It likely will backfire to relaunch it as DAREDEVIL: MAN WITHOUT FEAR or something else with a new #1 and a higher cover price. Marvel fails to realize what a "jumping off point" is, but their readers know it well, and know when to jump. ULTIMATE SPIDER-MAN's sales never recovered after Mark Bagley left. As you stated, those NEW X-MEN readers never returned. Fans look for any ol' excuse to ditch books and never return if you study sales charts.
There are several theories as to why Marvel and DC are flooding the market with high priced books. One is they cynically see the death of the direct market coming and greedily want to cash as much as possible before the cow is milked to bones for the last time. The second theory is greed and incompetence with the idea that the crash of 1993 will never happen and never be as bad. The third is the idea that creator contracts have genuinely become that expensive. The fourth is the collapse of ad revenue since 2008. Flip through any Marvel comic this month and, including front & back covers there may be about 8-9 ads. One of them may be for licensed merchandise, like t-shirts ordered online. Two may be ads to promote good living for kids paid for by nanny agencies, like Got Milk and Above The Substance. One ad may be for a video game. The rest will be House Ads for other comics (WOLVERINE #1 in particular has seen two ads within one issue). DC is faring slightly better, in that their latest issues have ads for React 5, NBC TV shows, Nintendo games, and Converse sneakers, but it still isn't as lofty as in 2006-2007. I remember once when I counted 21 pages of ads in a RUNAWAYS comic (which didn't include covers), I complained how it ruined the flow. Ironically, getting what I wished for may cripple comic sales for the big two.
The reason why Marvel may try a strategy with Daredevil that either will only work short term or not at all is simple. They have no other ideas. And DC isn't much wiser.