It takes longer to type and read. All the little seconds fiddling with the mouse, popup menus, hand eye coordination wastes your time and prevents muscle memory. Its hard to reach max throughput with long variable names.
Typing speed is absolutely not the limiting factor for programming productivity. If you are actually limited by typing speed, you are doing something very, very wrong.
Humans don't read words letter by letter, you recognize the whole word pattern. Abbreviations are actually slowing you down on this point, at least the first times you encounter each new one. Having a longest but more usual term will take you least time of reading treatment.
Autocompletion will rarely ask you to type more than four keystrokes for selecting any arbitrary long term.
Meaningful terms in context often happen to be far more easier to grep.
Except for sounding far more impenetrable to the lay man, there is not much left to these H4x0r turns. Of course jargon curse is not a prerogative of CS, this is a common spontaneous social behaviour.
