We talk about reasoning for Cereal in the article and in my case study too[1]. In large organizations, you often have tens or hundreds of designers, support multiple platforms (ios, android, web(mac, windows, linux) and do ad campaigns around the world. When it comes to typefaces, there really isn't any universal system fonts (other than Arial maybe), that are available on all platforms. If you use different fonts on each platform, the design will be slightly different, trying to manage a cross-platform design system (like we do [2]) becomes challenging. Every time, designer has to pick the right font, potentially do 2-3 designs with different font to make sure they all look how they want them to. Also then each time user or anyone in the company looks at the design on their device, it look will slightly different. If the marketing then also uses different type, it will look slightly off if you include product shots (one reason why Apple now uses SF everywhere). Short answer: having multiple fonts causes additional work and can confuse people, especially inside the company.
Since there isn't universal cross-platform fonts, it means you often have to embed fonts, and in some cases license them. Licensing fonts is different than just buying a font file. Even for small developers quality fonts can run up to $50,000 per app (imagine what the licensing costs are for a global company with large userbase!). With licensing you never get exactly what you want in terms of expression and functionality, and other brands can easily buy the same thing.
As the last point, what I find really exciting that we can now consider font kind of like a software. We change it whenever we find problems or just want to improve something. That is usually not possible with licensing. Obviously, you would and should only do your own typeface if you have these kind of issues and care enough wanting to solve them.