Google did over $100B in revenue last year. A $100M revenue product would move the needle 0.1%. And that's just revenue - it's pretty unlikely the net margins would beat Google's existing business lines. Meanwhile, it would require a significant amount of manpower, marketing, and support that would otherwise be spent on much larger profit centers. At a high level it just doesn't make sense - you'd need to be running dozens of such products to get any kind of return investors would care about, gumming up the org in the process.