Companies already do layoffs without commissions. They are always optimising to reduce salaries and increase profit margins. And its not "some number". Its the amount of $ brought in. Thats what companies care about.

Yes, but sales reps have very specific targets and sales managers have no problem routinely letting people go if they miss those targets. It really is a somewhat different situation from engineering--although projects, for example, certainly get canceled and teams let go. There's a more direct correlation to quarterly revenue/margin input in the case of sales.