The existence of sophisticated typographical tools like LaTeX and Word has rendered page limits effectively obsolete.
If I am instructed to write a 20-page essay, you can bet that my result will be exactly 20 pages, whether I write 4000 words or 6000. If I need to change spacing, the kerning will change, as will the margins, typeface and text size, line spacing and a myriad other factors obscured amongst my typesetting programs deepest, darkest, best-hidden commands. The amount of manipulation I have at my disposal is overpowering. Modern typesetting is as far beyond typewriting or hand scribing as an aircraft carrier is beyond a battleship.
Page sizes provide a guideline, yes, but little more, and this function would be much better served by word counts. Every word-processing program can perform accurate word counts, and there’s no way to fudge this statistic short of actually writing more or cutting content. Even markup typesetting like LaTeX can use approximate word-counts, without having to render the finished piece repeatedly, to see how long it is.
Anyone who has to submit work to a page count, I salute you: your ingenuity in manipulating your formatting is impressive. Anyone who requests that work be submitted according to a page-count, I’m sorry: your instructions are not sufficiently specific to achieve their desired goal.