The word “committee” is a long and tedious one to type or write; I can easily understand the motivation to invent an abbreviation.
When and why, though, did “ctte” become popular? What alternatives were competing with it before it became popular?
Moreover, what principle is at work, if any, in the choice of letters to drop? Most abbreviations drop a consecutive sequence of letters, either in the middle (“international” → “int'l”), or at the end ("regarding” → “re.”). This is obviously not the case for “committee” → “ctte”, so how did it come about?