They have filed for bankruptcy a few times haven't they? To be fair, I don't think it's all about losing credibility. The greater part may just be the shifts in reader habits. Going online is easier. The reviewers of the big online mags have CVs comparable to any of the major print mags rosters and comparable reference systems as well.
Stereophile feels half as thick as 10 years ago. Okay I'm exaggerating a bit. That's a lot less space for reviews and editorials. The recommended component list, one many waited for every year just doesn't seem to carry the prestige it once had. It's too bad. Like them or not, that list made things a lot easier for buyers with no access to auditions. It also launched many companies that really deserved the recognition.
Times are changing though. The "Majors" have serious competition. They just aren't as influential as they used to be.