You're confusing "obligation" with (very reasonable) "expectation" on the part of the public. Of course there is no obligation, and we have had many threads in the past about how the student-athlete, and in turn the coach or the AD or the communications staff, does not have to give out ANYTHING unless they feel like it. But it doesn't make it any less odd if precisely zero comment is given out on someone's extended absence.
Geno doesn't have to give out squat, either. But he chooses to, even in delicate situations like the Samarie Walker situation. He didn't go into detail, but he at least made mention of it, giving the strong impression that he didn't have much to say and likely wouldn't. Something along the lines of, "Yeah, she's working through some stuff. We hope to have her back soon." Or whatever. He didn't just flat ignore the issue.
Nan and the mods have made it abundantly clear that fans have no "rights" to personal or medical information. However, this is entirely distinct from having an expectation, formed in large part by the many athletic departments and coaches over the years and how they have chosen to communicate with the public and the fans, that someone would at least mention it and acknowledge the fact that there is an elephant sitting in the middle of the press room after a game. This is not the same thing as giving out personal & confidential info. No need to talk about being "morbid" here.
Fairfield Fan is exactly right. PSU or the coach should make a brief comment, however obscure, about the situation. Do they *have* to? Nope, not at all, so if they don't, then oh well, and it's not keeping me up at night. But there is no need to talk about "morbid" senses of curiosity. The implications of that kind of language are offensive. Some folks simply wonder what is going on. If on one hand we expect any major program to put up web pages on their athletes, maintain twitter feeds to talk about the program, help reporters put together stories as they cover the team throughtout the year and even in the off-season, it should come as no surprise that fans would have a distinctly non-morbid sense of bewilderment when players go missing.