The annual sales revenue of adidas is 19bn US dollars - that's £10,000,000,000. Nike is 50% bigger than that again.
These deals are not about shirt sales, they are about advertising because their logos appear in masses and masses of print and internet media along with primetime TV - the value...
Well, for these sort of clubs the number of shirts sold is largely an irrelevance to the sportswear brand.
The next meeting adidas has with Real Madrid could be fun, though.