good bye customary at workplace in japan

hey guys/girls,
this is some kid working in software company at osaka.

i've been here two months
now and what i've noticed is that people sitting beside me or nearby just leave without saying good bye or see you tomorrow :p

I thought it was somewhat
disappointing not to get any byes from'em, but was wondering if it's a customary not to bother anyone working when you're leaving first?

or is it just a common sense? your reply would be appreciative :p

I don't think it is a common sense/practice not say anything to your colleague before leaving. We often say "Osaki ni" and "Otsukare sama."

They must be just shy :(

How about saying to them "Otsukare sama"? Then they will respond to you by saying "Osaki ni" or "Good Bye." And over the time, they will start saying to you "good bye" even before your saying something.