I think that it’s the perceived rate of progression coupled with a lack of math skills that make people think that 5/3/1 isn’t for beginners. They see a program like SL5x5, where you start with the bar and add weight every session and compare it to adding weight every month. They don’t consider that a beginner on 5/3/1 wouldn’t start with the bar and that’s it.
Instead, you’d do a bit of pre-planning by going to the gym and attempting to figure out a reasonable real life max before calculating a training max. For most people, that real life max is going to be a weight that would take several weeks or more to reach with the progression in the 5x5 program.
When you get beyond that point, you have to consider the feasibility of continuing to add 5/10 pounds per session, for 5 sets that are all at that new higher weight. That’s where, for me, 5/3/1 has been great. Working at the submaximal weights, I’ve never stalled and the weekly PR sets keep it fun.
For me, the inevitable stalls of a 5x5 program would have been frustrating and demotivating. To be clear, I’m not saying that anything is wrong with a 5x5 (or other beginner) programs but they’re not the only, or even the best, way for everybody to start lifting. Different people, different goals, different ways of meeting those goals.