Can’t remember what old coach said this, but the quote was something to the effect of “If you have too much of your depth on the field at once then you will feel like you have bad depth.”
Teams have good depth for an injury here and there, but when half your lineup is a mash unit, there is no fixing that.
No one is trotting out an entire second team of seasoned vets.
Depth pieces are less exposed when sprinkled in among mostly starters.