Guess this must be a question about weatherlink.com?
Don't know I'm afraid. Suspect this is a question that only Davis Support can answer.
My only guess is that maybe this Notes field is intended for a short additional note about the location of the station rather than an ongoing log of station issues. So it may be limited in length to eg 200 or 500 characters or some such, or maybe isn't expected to be indefinitely editable. Certainly, the window provided is quite small suggesting that not much text input is expected.