why is it so difficult to get a letter of recommendation?

Im enrolling In nursing school lpn to rn program and for some reason its so difficult to get anyone to write me a letter of recommendation. I havent burned any bridges im a good nurse so whats the problem? Ugh one nurse told me she is swamped with work but she didnt say no. My nursing supervisor never called me back. Im just frustrated by it all. Is this normal behavior or theyre just not interested in doing it?
At some facilities, there are rules that recommendations or references can come from HR only - NOT just any individual employed at your job (this stops someone writing a reference based on the 'buddy system'). References reflect the facility's reputation (and the provider's credibility), so you can see where a phoney reference for a 'bad' employee could reflect poorly for the facility if a false 'glowing', 'wonderful', 'terrific' reference influenced the hiring/admission decision. And in those facilities, the referring employees can be disciplined for deviating from P&P.I take giving recommendation/references VERY seriously for the reason that I am giving my 'vote' of confidence for that applicant. To be brutally frank, I doubt some people will EVER be good new employees and/or students anywhere. They're NOT good employees/students HERE (as I know them), and I don't feel I should be writing a falsely positive reference (not even a vague one) just to push them off on someone else. There's an old saying that "if you can't say something nice about someone, don't say anything..." I don't want someone to say, "Well, this person, amoLucia, recommended her. What a mistake!" It's my reputation (and credibility) on the line here. Now maybe someone else has a different opinion, but they can write that letter.I have written some references. But I am ever so careful and I give great thought to WHOM/WHERE the reference is going. I am very clear as to WHEN I knew the applicant, for HOW LONG, and in WHAT CAPACITY. I have NO IDEA of what kind of worker you are and how strong your nsg skills are. But as a student in my Medical Terminology class you were a good student and that is all I can discuss and elaborate upon. See what I mean?So to answer your concerns, there may be several reasons why references may not be forthcoming.

Thank you for taking the time to explain