The fashionable new weapon in the war between authors and program committee members is line spacing.
In previous skirmishes, padded page counts, tiny font sizes, multiple columns, and narrow margins were very popular. But the program committees for the major theoretical computer science conferences, wise to this trick (all authors themselves) outlawed those tactics, and decreed that submissions must be in an 11 point font, single column, with one inch margins, and with ten pages of text not counting a title page and bibliography (that way, we don't encourage authors to trim their bibliographies and hurt the citation counts of the PC members, nor to trim their abstracts and make the PC members actually look at the paper itself).
So now, suppose you've written the first draft of a paper describing your latest greatest newest result, and it's 45 pages. What do you do?
Well, you could carefully read through the paper, considering which of the results the program committee members need to see the details of, which they can be expected to take on faith, and which can be omitted altogether as unimportant, and get it down to 21 pages. Separate out the title page and bibliography, leaving 17 pages of actual text. Reduce the size of a few figures (you do have figures, don't you?), place some figures side by side, and again consider which of the rest might be necessary, getting it down to 14 pages. And then read through the whole thing even more carefully, thinking hard about which phrases and sentences are significant and meaningful and which are flab that can be reworded in a way that both reduces the length and makes the whole more intelligible, and with effort get it down to 10 pages. (As an aside, Wikipedia writes that Leonid Levin is "well known for his work in randomness in computing, algorithmic complexity and intractability, foundations of mathematics and computer science, algorithmic probability, theory of computation, and information theory" but another thing he's known for among former program committee members is writing very very concisely. Too concisely, to the point where his papers became difficult to read again. But to a point, more concise writing can also be better writing.)
Or, you could split the paper at page 15 or so, arbitrarily, and call the part after the split an appendix. And then you could use a format that packs 20% more lines per page, by reducing the spacing between the lines. It makes the paper much harder to read, but it's not disallowed, so it must be ok, right? And then you could submit your paper, now at about 12 1/2 pages of text, figuring that the 10-page limit is never really enforced. And your first draft becomes ready for conference submission without all that hard work.
Given the difference in effort required between these approaches, and the pressure of writing to a deadline, guess what happens?