Also not a number theorist...but I'd bet those so-called experts had invested far, far too many of their man-years in that unproven conjecture. All of which effort and edifice would collapse into the dumpster if some snot-nosed little upstart like you, using crude computation, achieved overnight fame by finding a counter-example.
(If I could give my many-decades-ago younger self some advice for math grad school, one bit of that would be: For any non-trivial "Prove X" assignment, start by spending at least 1/4 of my time budget looking for counter-examples. For academic assignments, that's 99% likely to fail. But the insight you'll get into the problem by trying will be more worth it. And the other 1% of the time you'll look like a genius. And - as soon as you attempt real math research, those odds shift enormously, in favor of the counterexample-first approach.)