Language just changes over time. There was probably some point in history where some abbott was annoyed that the young scribes were writing "here" instead of "hither". Also, if you were going to design a new language from scratch, would you really use words like "through" when "thru" is perfectly sufficient? There are lots of holdovers from earlier times. The only problem is when you misspell words with one letter.
Besides, you're on the internet. You should expect a certain level of short-hand. Any proper grammar and spelling you read is a delightful boon. Not that I don't prefer proper and complete sentences, but I don't necessarily expect them.