AMC is one of the more aggressive stations in not letting its content out to other streamers. You can't watch... oh I don't know, Interview with the Vampire anywhere else, other than having AMC on linear TV or having access to their associated video-on-demand. I remember having to cast around to find the (pretty good) John le Carre adaptation The Little Drummer Girl anywhere after having missed its initial broadcast: I ended up getting the free trial of Sundance Now, which is more or less AMC+'s predecessor... or something like that.
But: most of what people most want to watch is stuff that's on legacy deals, or that they're letting out older seasons of, or just don't control. Like, Better Call Saul is on Netflix, but not the current/final season. I feel like the era of them really jealously guarding their shows to try to make AMC+ work has coincided with a bunch of stuff people aren't that interested in seeing (and maybe the stuff people do want to see they don't fully control).
Lodge 49 is cool (but ultimately quite niche, I think), but they don't have an audience clamoring to stream Low Winter Sun or whatever.
What? Disney+ and Prime are much worse. You can't find a single show anywhere else. I would say AMC is one if the better in this regard considering both BB, MM, BCS and TWD can be watched on a plethora of other services.
AMC is basically trying to act like it's Disney+ or Netflix, or whatever you prefer, for its own content. Their issue is just that the stuff from them people actually want to see in big numbers is more or less that list you mentioned. They don't actually control Breaking Bad, Mad Men or Better Call Saul. The Walking Dead and Fear the Walking Dead seem to be on legacy contracts that give all the "back" seasons to Netflix and Hulu, respectively.
They haven't had anything new that people actually care about enough to notice its exclusivity. The newer Walking Dead spinoffs would be about it, I guess.
The article mentions that AMC does not actually own the rights to several of their most well-known shows (Mad Men is owned by Lionsgate and Breaking Bad is owned by Sony).
