As I have noted on other occasions, the style/convention in mathematics, at least in my part of that world, is that advisors rarely, if ever, have, or insist upon, or accept, co-authorship of any sort involving their students' theses and related publications. In recent years I have seen a few examples, but this already surprised me.
That is, in my experience, in the best situations, and barring a handful of truly exceptional students, of_course the advisor had a very good idea of how things should go, knew the key background, knew the pitfalls, ... and most likely could have written the thing up in an afternoon if they had nothing better to do... but they did have better things to do.
It did take me some time to fully understand the extent to which this is true in my field... since I, too, had bought into the mythology that beginners can become experts within a few months or a year or two, thus "bearding" their advisors. Well, I don't think that really happens in the way novices, especially, seem to want to believe. That is, an experienced expert can "catch on" soooo quickly to new facts that they operationally nearly-instantly assimilate that information, and integrate it with previous. And, unlike the novice, the expert can often see implications far in the distance...
So, again, in the part of the math biz within my view, of_course the advisor has made a significant contribution... and, of course, there's no point in making the student "acknowledge" this by giving up some publication credit. Indeed, it seems that if a thesis gets published with advisor as co-author in math, it suggests that the student really didn't do much work at all... and is being dinged for that.
I am fairly consistently amazed at the seemingly-popular notion that some PhDs are done "independently" of advisors. Sure, some advisors may be technically incompetent... but how does a novice do something worthwhile that experienced experts would have wanted to do, but tried and failed? Does one have to be "The Chosen One" to do a PhD? Or are some fields so shallow that complete inexperience, or two months' experience, really makes an expert? Or is that merely a popular myth here, as well as elsewhere?
And, back to the original question, and as in other answers: don't try to coerce people to do things you cannot happily defend. Further, do not pretend that beginners are or should be on the same playing field as seasoned experts, nor that the experts should always "be sure" to grab credit for every little thing their apprentices manage to do under their guidance.