Speaking from MY history.
I spend a lot on willy nilly accumulation. Since....1986! Slow, a few things every year. then a "frenzy" when LGB went under, and there were things that suddenly had appeal. Over time i have US, German, french, Hawaiian, standard gauge, narrow gauge, DR, amtrak, pink, blue, yellow, chartreuse, Aster, roundhouse....
I have far more than i need to operate a plausible, themed railway.
I was devoutly narrow gauge....until the LGB F7 and Genesis, bought em , run em, but still model ng....but they were a must have. Ditto saxons, etc
I think with 1-2 locos, a rail truck or trolley or motorcar, some freight stock and coaches, and one could have a splendid small system, 2-3 structures, etc. it doesnt take a lot to create a meaningful stage for trains, but instead of a backwater, we want Chicago.
I fell hard for LGB marketing. Less so marklin's. Its easier to buy new trains than anything else in the hobby. And, in part, my behaviour was the result of LGB not consistently offering basic stock every year, ie i want a DRGW box car, coach, always available so i can build a DRGW themed layout. different paint jobs every year. Either buy it all at once, or wait a decade.
Part of my joy is building and painting, making scenes, and starting a new one.
But stuff inspires me.
There are many who accumulate in anticipation of "one day".
Planned , informed, and mindful buying can save a lot.
If i could wipe the slate and start anew, perhaps On3. Hon3?
Frankly n scale is much less, z scale , not at all, but neither require much space.
G takes a lot of space, landscaping, etc. and, contrary to OP, imho, g scale has the least amount of variety and accessories, all of which add to realism, and, cost.