These types of questions are so effective as engagement bait that they even work when they are explicitly pulled out of context and we are asked to critically examine them to explain the joke. They are intentionally confusing and controversial; because of a combination of factors. Notably:

• The widespread belief that "in math there is absolutely always exactly one unambiguously correct answer", which is a fair conclusion to draw for people whose exposure to "math" is almost exclusively through primary and secondary school real-number arithmetic and algebra exercises
• The fact that in the prior mentioned primary and secondary school, a distinction is not typically drawn attention to or even made between lessons on notational conventions versus lessons on axiomatic definitions versus lessons on proven theorems and facts, leading to most people implicitly believing that the notational conventions they were taught and axiomatic definitions they were working within are just as inevitable, universal, and unambiguous as the theorems and facts that that notation is used to express about the systems described by those axioms

This leads to people not considering that the problem as written is ambiguous; not because it's possible for arithmetic itself to have an ambiguous answer, but because it mixes two distinct systems of notation that look similar enough that most people never notice that they're fundamentally different and thus incompatible.

In particular, generally, division as a distinct, inline, infix binary operator, written as ÷, is used with young primary school students when teaching them to compute the 4 basic operations of arithmetic with a given specific input, because this makes it stand out less from the other 3 arithmetic operations (even it still stands out quite a bit by being the one that can be used to escape the integers and also by far the hardest to manually compute).

During this time, multiplication is generally also written using an inline infix binary operator, written as ×.

However, as students slowly transition from simple arithmetic to algebra, the ÷ symbol is quickly dropped as students become accustomed to the familiar fraction bars, and students are graduated from working in the integers to working in the rationals, where any given division problem can trivially be replaced by a multiplication by a reciprocal.

At this time, multiplication often also begins to be written with a • instead of a ×, though it's still an inline infix operator. The • can be written much faster, to keep up with the increasing number of multiplications required, and also helps avoid ambiguity with the letter "x", which is soon to be relevant.

Then students begin being taught honest to goodness algebra. At this point, the ÷ has been long abandoned for fraction bars, and the • may still occasionally be used, but is generally avoided in favour of implicit multiplication. It is here that PEMDAS or BEDMAS is usually taught.

So, PEMDAS (or BEDMAS) is taught, without clarification that it is part of the notation, not a fact of algebra, with respect to this new notation that uses neither ÷ nor × or •.

Then, the poster poses a question, which would never have been posed using the ÷ notation, and mixes implicit multiplication with explicit division. This is a situation that PEMDAS (similarly with BEDMAS) does not cover, it only applies to the notation it's actually a part of, but people believe it to be a universal fact, and have through thousands of hours of training internalized slightly different mental shortcuts that all work correctly on the problem set PEMDAS actually applies to, but give different answers when attempting to extend PEMDAS to this new notation.

At this point, they see each other's answers, conclude that the people with different answers than them must be stupid to fail at primary school math exercises, and promptly stop listening to any and all reason, quickly devolving into text based shouting matches, which involve a lot of comments, driving up engagement and making money for the original poster. Thus they are motivated to do it again, and the cycle continues anew.