There are some consistencies in letter patterns, just not in individual letters. For example, no word that starts with go-, ga-, or gu- pronounces the g like a j (except for the archaic gaol, and there’s a reason the spelling was changed to jail). It’s mainly limited to ge- and gi- words.
Inconsistencies with the other options are probably due either to how the term came into English (English is practically built on loanwords) or some other subsequent pattern of letters I’m too lazy to try to identify.