Because it's largely not an experimental science, but rather is groups of people convincing themselves they know what someone is talking about. As the article

Because it's largely not an experimental science, but rather is groups of people convincing themselves they know what someone is talking about. As the article pretty much says. The article also suggests an "exceptionalism" of maths in that their results hold up even when their methods don't. In other words math papers are full of "unimportant flaws and errors" but even though that's the case when corrected or verified, somehow the conclusions of the papers mostly hold up, in the author's opinion. But I tend to think this is more because, math is groups of people (and formal verification systems) convincing themselves they know what someone else is talking about, so confirmation bias is probably in effect. The limitations of a self-consistent set of axioms after all... You may say that formal verification systems are perfect oracles... But if papers have "unimportant flaws and errors" it's possible that those systems have them, too, right? It's also possible that as those systems were written by people, they reflect and somehow seek to confirm the biases of those people or their understandings (or misunderstandings) about mathematical knowledge. So I don't think maths is quite as exceptional as this author hopes it might. Tho Maybe it is