A small number of the leaders of the IT industry. There are many other leaders in many other industries and not all of them are for staying in the EU. I suspect all of them will make sound logical decisions based on what they think and perceive and believe will help their personal interests. I also suspect all of them will make their decisions based on what they are told to say to keep the the status quo so that their personal interests are maximised.
Occam's Razor and all.
Or am I being a bit too cynical?