Think of each wholly own as a franchise. Make no sense to join them together unless you like seeing sticks and stones flying.
Plus you have 3 different managements. And CEO's hate to cut managements jobs. Can you imagine being in a upper level position and had to join the 3 groups? If you were in charge you would have 3 times the amount of work. And for what? I doubt you would get paid anything additional. I guess my point is: Management hates work. They want their 10-3 m-f jobs. Anything additional is like working for free.