datteebayo is an regional dilect of the impression meaning - Because.
for example, lets have a conversation you strike me an obvious question, iceT why is your fg so low - Because.
dattemo, because, Datte, because, Datte doushite, but why
it's sort of between but and because, depending on regional dilects, and depending on terms of use, the use alone such as provided is purely meant as a comment
such as the meaning of the word wouldn't be in any dictionary., (maybe it mite be who knows pshsh_)