I, too, am not surprised by the possible demise of Charlie Brown specials on broadcast television. I felt as if the end was looming a few years ago, and now it's finally come. 53 years is an incredible run for Charlie Brown specials, and very few non-current events shows that have or will have been on the air for 50 years or more likely stay around for a few more years. This may apply to the remaining long-running daytime soaps and Sesame Street (the latter will no longer be aired on HBO Family as of November 1). Though a very small number of non-current events programs will likely have plenty of life left, particularly The Price is Right.
But, regarding Charlie Brown specials, I think this sounds like a case of ratings having fallen in recent years. There have been no brand new Charlie Brown specials in nearly a decade (2011 was the last new special, if I recall), so this could be hinting that the Charlie Brown specials were likely falling out of favor.
Not only could this be the end of an era for Charlie Brown specials on television, but also the official end of an era for animated cartoons for children on ABC. The network had discontinued non-educational Saturday morning cartoons in September 2006, leaving only the occasional Charlie Brown specials in primetime (possibly due to contract reasons). ABC's contract to air Charlie Brown specials may now be expired, and by the looks of things, ratings have been in decline for the last few years, and ABC may no longer be interested in airing these specials. I don't know if ABC even airs any cartoons on Saturday mornings nowadays, if educational in nature.
Plus, it could be possible that the popularity of Peanuts is likely in decline. There have been no new strips since 2000 due to the creator's declining health (and eventually death) at the time. There was a package of syndicated reruns of strips with packages covering 1959 to 1974, and the 1990s. My local newspaper did publish the vintage strips until 2015 when they decided to introduce many new comic strip series. Three strips published prior to the overhaul retained staying power, but by last year there was another comics page overhaul and those three strips are now gone.
I also think most of the fanbase who grew up enjoying Peanuts are likely grandparents now, and those fans that grew up with the franchise are likely deceased, or getting so close to death, thus shrinking the fanbase and ratings for the holiday specials declining.
Also, to the OP, aren't you actually referring to ABC?