When your turnover is into 9 figures a year then you’re not a person anymore. You’re a business.
Mille probably pay/give Nadal stuff to be associated with him. The people he must meet probably look at his watch and go “who makes that? 20g in weight you say? Can travel to Jupiter you say? I must buy one for myself old chap” and tell their lackey to go buy one for them. If a couple of people do it, then perhaps its worth giving him a free watch? Make no mistake, the type of people they get to meet are in a different league!
I counted 7 people in Muguruzu’s on court support team and she’s what? Top 20 in the womens. Someone like Nadal easily employs twice, maybe thrice that, maybe even more.