Linguistically. The former words, "pre-adaptive" and "pre-adaptation", were exaptated into the more impressive sounding words, "exaptive" and "exaptation".
And while these new words seem clumsy and serve to obscure meaning, it behooves grant-gathering science to sound important when they mumble the holy rites of their particular trade.

Yeahbutİ, exaptive and exaptation say what they mean, pre-adaptive and pre-adaptation don't. On a clumsy and obscurantist scale I would put pre-adapt well above exapt. If pre-adative and pre-adaptation meant anything at all, they would mean that they started out useless and only took on a use after being fully formed.