The only free and comprehensive online etymological dictionary of the Spanish language
gustar (Verb) "to please," "to like;" "to taste"
13th cent. Old Spanish gostar. From Latin gustare "to taste." From gustus "tasting" (see gusto).
Portuguese gostar, Catalan gustar, French goûter, Italian gustare, Aromanian gustu, Romanian gusta, Sardinian gustare

Over time, the meaning drifted from "to taste" to "pleasing (in taste)" to "pleasing."