I'vE bEeN ScRoLlInG ThRoUgH YoUr mOtHeRfUcKiN MiRaCuLoUs gRuBlOg, BuT I KiNdA GoT A QuEsTiOn tO AsK Up iN AlL ThIs. HoW CoMe i dOn'T GoT NoNe oF ThOsE MoThErFuCkIn' BuBbLe gHoStS? i tHiNk i hEaRd sOmEtHiN' aBoUt mE AnD BeInG AlL Up aNd mOtHeRfUcKiN' cAuSiNg dOoMeD TiMeLiNeS AnD StUfF. i dOn'T LiKe tO ThInK I CaUsEd aLl tHaT ShIt. I MeAn lIvE AnD LeT MoThErFuCkIn' lIvE. :o(

It’s because Gamzee is effectively immortal due to plot armor bullshit. So basically Gamzee’s in doomed timelines don’t die before the timeline is erased so he gets erased along with it.