It's because the storytelling needed for Wall Street. It's the only way to get sky high revenue multiples, selling a dream, because if you're a conglomerate all you can do is to sell the P&L - it's like selling an index. If you have a business division that's does exceedingly well compared to the rest, you make more money by spinning it off.

I think Asian companies are much less dependent on public markets and have as strong private control (chaebols in South Korea for example - Samsung, LG, Hyundai etc).

If you look at US companies that are under "family control" you might see a similar sprawl, like Cargill, Koch, I'd even put Berkshire in this class even though it's not "family controlled" in the literal sense, it's still associated with two men and not a professional CEO.