What kind of answer would satisfy you? It seems that you're being dismissive of the very reasonable responses here.

In short, standards exist because IBM built the original PC in 12 months using off-the-shelf parts and published the full technical specs...obviously copycats took off with them and reverse-engineered the bios.

IBM did try to close it when they launched PS/2 with Micro Channel architecture (proprietary, with licensing fees). The industry formed a consortium and created an open alternative, which was bad for IBM.

The colorful boxes exist because there's a profitable consumer market for components, which exists because the standards remained open, which happened because the industry defended them against the company that created the platform. Maybe this clears things up a bit.