AND
Not only what everyone else has said but even if you DO manage to upgrade and kinda sorta get what you’d like — even on a base.
Rosters don’t really exist; trips are rostered with reserve preceding them and extra open assignable days trailing them. The trips are placeholders for a reserve window with assigned duties that can vary wildly.
So whar you essentially have is a reserve roster.
Picture spending your entire career — regardless of bid, preference, or seniority — on a reserve roster. In a sometimes long haul operation transiting multiple time zones with multiple body clock swaps.