It’s hard to reliably hear the difference between gwu (“gwoo”) and gu (“goo”).  So if putting a word together would get you /gwu/, the language naturally simplifies it to /gu/.  For similar reasons, any time you might get /ugw/ at the end of the word, it can be pronounced either as /ugw/ or as /-ug/.  But then if more is added to the word, the full /ugw/ will always be pronounced, since it’s not at the end any more.  Same goes for /uggw/, too, so we say

gesalugg            ‘we (you+me) love h/her’

but then adding -ig, to refer to more people, we say

gesaluggwig        ‘we (you+me) love them’