If someone with millions or billions of dollars doesn’t have an official API after operating for years, that’s because they don’t want to have one. You may receive a Cease and Desist letter, or they might block your IPs, or just scramble their markup in ways that are hard to figure out. Whatever their approach, they likely have more money and manpower to throw at stopping you than you have to evade them, especially if you’re doing this to multiple large and powerful companies.