By themselves, "businesses"
don't like to create new companies. But businesses aren't sentient, so it's actually two different groups we're talking about:
1. Executives generally don't want to have separate companies. Having it all under their purview gives them more power and control.
2. Shareholders often want separate companies, especially when they perceive one division as being much more valuable than the rest. With separate companies, they can own the profitable division but not the others.
The balance of power between these two groups is why ends up dictating what happens. This is why Google was able to turn into Alphabet (a single company) instead of spinning off their non-core assets (as some shareholders desired). Unfortunately, Yahoo executives just don't have the clout to hold together any longer. The market thinks Yahoo's assets have negative value: the only thing propping up their stock is their investments, and shareholders want to hold those investments by themselves.