There's no real explanation. The verb пасува́ти is used either with a person in the dative case, or with «до» + other item of clothing with genitive. It's just the way this verb is used.
Some other verbs with similar meanings also use the dative case: годи́тися 'be of use, be appropriate', підхо́дити 'to be suited for'.
In Ukrainian it's a bit similar to German, where Dative case is also often used with verbs, like Mir ist kalt, Mir gefällt, etc. This verb is one of those that demand a Dative.