You don't know that. It could be that Madara was strong enough to gain some control. Itachi was able to break out too, and he wasn't given such freedom. It seems to me that Kabuto bit off more than he could chew summoning them.
Itachi too had some control over his emotions, and same with Madara. I'm talking about this mode, where they coudn't even speak or think for themselves:
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In all these cases, Kabuto has full control over his Edos. And btw, Orochimaru could control Hashirama like a mindless puppet. I'm sure Kabuto who has both Orochimaru's chakra, and his own, can control Madara fully.
EDIT: Ok with Itachi's case, it's different. Itachi used KA to break out of Edo Tensei. Madara used some handsigns.
If Itachi had not implanted that crow into Naruto, Itachi would have never broken free. It was just very convenient (aka plot) that he could break free at that point. As far as I'm aware, Madara does not posess KA, and he also does not have a crow conveniently hiding in Naruto to break him out. Madara only has the knowledge of the correct handsigns to break him out, and he could only use those seals because Kabuto wasn't fully controlling him at that point.