Popularity of Inner Carbon Blades

I recently noticed that many top players are using Inner Carbon blades as opposed to the faster Outer Carbon blades, (e.g. Ma Long, Ovtcharov, Franziska, Harimoto.) 

This may appear a bit counterintuitive - given that the new polyball is slower, you would expect players switching to faster outer carbon blades or even the likes of primorac carbon.

My theory is that what's going on here is focus on spin rather than speed - the bigger ball is slower, yes, but it's also harder to spin. The more woody soft compositions would allow more dwell and hence enable better spin capabilities. 

Do you think this is the main reason? Or is there anything else to it? Do you have a preference over inner or outer carbon blades and if so why? 

Yes, I think getting more spin is the reason. If you listen to Ovtcharov, Apolonia or Franziska reviewing their blades with TTD Dan, that's one of the main things they talk about. I think it's Ovtcharov who says he needs an inner carbon blade to attack low balls with full force and still get them to dip onto the table. (To be fair, Timo says the same thing about his outer carbon blade in the context to explaining why he doesn't use one of the super ZLC blades). 

I used a Viscaria for years until switching to a Franziska inner carbon to get more spin. It works for me. The one thing I have more trouble doing with the Franziska is driving rather than looping third balls. As that's an important part of my game, I eventually switched to an outer carbon Freitas (like a slightly thicker Viscaria with limba instead of koto outer ply) which seems like a good compromise for me.

If it is true that top level players can produce more ball speed than they need with innerforce type constructions, they have no reason to have composite right under the top ply. 

Correction: if they want to, that's a good reason enough :) best is what's they feel best as long as their choice does not impair any compartment of their game.