Because we're lazy. I mean, just look at how many people are too lazy to type "be right back" and use "BRB". Or, G2G, LOL, C U L8R or 2nite. It's because we're too lazy to spell things out.
On an episode of Friends, Rachel made a comment about mincemeat pies and then said British people put weird things in desserts. Do you really not know what mincemeat is? :wave2: