It's entirely a business decision that's profit-driven.

There's nothing technically limiting these manufacturers from making reparable devices. It may extend their development cycle by a month or more for a product though, as they need to settle on standardized parts, keep stock of materials for repair, produce readable manuals, and make alterations to make components accessible.

It is not in their interest to make any of this available, and it is entirely in their interest at the same time to discourage repairability, through marketing of new products and suppression of right-to-repair movements.

Ironically, a right-to-repair law would at least put everyone on equal ground as far as having to comply to a minimum standard. But tragedy of the commons and all that.