"As an individual, I can't simultaneously develop 10 different products, but a large company sitting on billions in cash could develop 1000 niche products simultaneously."
Because the question faced by large companies, and even merely medium-sized and small companies, is not what can we do, but what's the best thing to do.
If I've got a product line with 100 engineers that is making me a million per engineer, and I've got a product line with 5 engineers making a quarter million per engineer, and I decide I'm going to hire 10 more engineers, even though it is true that I can't guarantee that the scaling numbers will hold when I add more engineers, it is still often the rational choice to assign those 10 new engineers to my very profitable product. In fact it can make sense to eliminate the product line with 5 engineers and put them on the really profitable product. The fact that I could do 11 projects with 10 engineers each isn't very interesting because odds are that the other 10 projects won't be as profitable, and I won't get anywhere near as much money.
Meanwhile, some other company in the market might very happily take on the less profitable, but still profitable, smaller niche. They can do it with different degrees of overhead, maybe in a different cheaper location, and perhaps with fewer compliance requirements bearing down on them, etc.
There are, of course, endless, endless nuances and "what ifs" you could play. This comment is not a course in resource allocation for business. It's just a comment intended to point you in the direction of answering the question "Why don't GooFaceZonaSoft do all the things?" in a reasonable manner. It also explains why GooFaceZonaSoft still acts resource constrained quite often, and why despite the fact the tech industry tends to develop very large giants at the top there's always, always a ton of smaller companies and there's never any risk that the entire industry is all going to consolidate into one big company, because the first thing that mega corporation would do is divest a ton of the less profitable sub-businesses, which would promptly reform externally.