Nike won't dictate but I'm sure some deals are getting pushed a bit by sponsors. I'm actually pretty surprised, though not sure if it would be allowed by law, that Nike and Adidas are not putting lot of clauses about players being able to move only to clubs they sponsor too. It's pretty odd to see some of those brands footballing icons like Messi, Ronaldo or even Pogba playing in kits their biggest competition sponsoring. I can't see business point of view there. You spend millions in marketing through some player yet he runs out on the pitch with much bigger view of your competitor's logo. Though if I'd be in charge, I'd ban players wearing other brands than club sponsoring ones on the pitch too, though that's completely new story.