Why do Rabbis love to answer questions with “Its not recommended”?

rabbi1I hate when I ask a rabbi something and instead of saying the don’t know, or telling you they need to look it up they say “its not recommended” I hate this answer because it just leaves you hanging without any real knowledge, they say it all the time and it bugs the crap out of me. Questions like what do you think of showering on yom tov always elicit this response. Why do rabbis do this? Why cant they just say they don’t know or they will tell you later?