Presumably a lot of pro dancers don't want to associate themselves with Strictly though? Or don't have the time to take away from competing.
I am still vaguely hoping they might bring Nicole back this year. It's difficult after the NOTW article, but they did apologise for it so in theory it shouldn't matter, don't know what the reality is. Also if it's true that they didn't invite her back because they didn't have anyone to pair her with, that actually kind of makes sense- if Hayley was who they asked instead, there's no way they could have partnered gigantic Mark with tiny little Nicole. And of all the shorter ladies, Nicole is perhaps the least well known and possibly the only one they could not invite but still get her pro partner to take part.
I wouldn't want to see Ian dancing with Hayley, Hayley's latin dancing is not in Ian's league at all. Although they would be much nicer to watch dancing ballroom than Ian with Camilla.