It's downvoted because it reads as though IBM made a mistake the commenter thinks they should've never made, as opposed to a mistake from IBMs perspective given their business strategy at the time.
That is, it appears to tacitly agree with, and chide IBM for failing to defended, closed, walled-garden ecosystems.
That's certainly not what it seems they meant. It's just how one might initially read it and downvote.
It was certainly a mistake to base the original IBM PC hardware design in easily obtained electronics, and hope the BIOS copyright would be enough to hold out clones, unlike previous IBM hardware.
But it's not their mistake at all there is nothing they could do, companies went out there and reversed engineered BIOS. They couldn't possibly stop them.
That is, it appears to tacitly agree with, and chide IBM for failing to defended, closed, walled-garden ecosystems.
That's certainly not what it seems they meant. It's just how one might initially read it and downvote.