Unfortunately, it seems that most of the time it's because they are lazy sheeps who don't even have a clue of what means 90% of the abbreviations they use, but

Unfortunately, it seems that most of the time it's because they are lazy sheeps who don't even have a clue of what means 90% of the abbreviations they use, but don't want to look like the sole ignorant in the room asking it, and won't take time to look at it by themselves later, even for the 10% they most often encounter.