His mother came from money, being the daughter of a banker, and the granddaughter of a banker. His father was a lawyer who founded a law firm focused on corporate law and technology law. Given that his mom knew Opel personally, and his dad was a technology lawyer, is it any surprise that Gates' first contract with IBM was so incredibly friendly to Microsoft's interests?
In addition, IBM was under pressure at that point because it was being sued for antitrust violations by the US government. That limited how aggressive it could be in new contracts without drawing extra attention. In other words, the antitrust effort from the US government took power away from IBM and allowed for new companies to flourish. Then about 20 years later, Microsoft was sued for its own illegal use of its monopoly (a trial at which Bill Gates lied on the stand, and where Microsoft falsified evidence), and this work to limit the reach of Microsoft allowed for the Internet to flourish and led directly to the rise of companies like Google and Amazon. It's now time for another round of antitrust to allow more companies to flourish -- only hopefully this time the antitrust efforts don't fade out and are aggressively pursued year after year so we don't get more shitty monopolies making things awful.