It's even worse than that. If a show has a budget of $4m/episode. That gets spent lets say $3m/episode variable costs and $1m/episode amortizing fixed costs. If the show only has 10 episodes, then its budget needs to become either $3m variable plus $2m amortizing fixed or more likely $2m variable and $2m amortizing fixed. So cutting the episode count either forces more to be spent per episode or forces fixed costs to take up a higher portion of the budget and results in even less money for variable costs(ie fx).
You can argue that cutting the episode count helps creatively, but from a budget perspective it's a disaster.