First of all it should be said that many enthusiasts and some tourists don't feel the need to traverse the Zermatt - Brig - Chur route by Glacier Express itself. The normal trains on the line are just as good (and cheaper) , the views are the same.
Many long distance tourists (ie from Asia and the Americas) no longer do the whole 'belle epoque' journey from end to end, because they are not being transported - like the 'belle epoque' era Brits - between the 'glamour resorts' at each end. Modern tourists are much more likely to want to do the Glacier Express and end up in Zurich for a flight home (or such like).
If you want to do that, you can do the popular 'short version' trip which is Brig - Chur. This is fine for 'general tourists', however, for railway enthusiasts this short run is not ideal because it omits the Albula railway Chur - St Moritz with its loops and spirals.
Zurich and any other place north of the Alpine chain is not a good stepping off point for the Glacier Express. So overnight locations along the east - west axis along the south of Switzerland are best, eg Brig. Brig and Chur are not popular 'resorts' with most tourists so the hotels are fairly economical. This benefits railway enthusiasts who often favour 'convenient for train travel' locations over 'famous scenic' resort locations.
Looking at the route from an West - East perspective:
Because Zermatt - Brig is the least 'amazing' section of the route, Brig - St Moritz is a good compromise. Booking the GEX from Brig makes it possible - with early start - to reach the GEX from further afield eg Bern or even Basel. On reaching St Moritz, one can stay in somewhat more 'budget-friendly' places such as Samedan or Bever.