I think the issue is hard to understand if you aren't aware of the nitty gritty of ward set ups.
I'm a mental health nurse. If I am with an unwell patient who is on eyesight observations I cannot pop to the loo - I need to be with them and alert constantly. If there is not a colleague free to swap with me I cannot leave. And since staffing is terrible (like, my current team has less that 50% of the nurses we are meant to have) the chances of someone being free to swap are low.
Now, if I am looking after a group of patients who need to be checked regularly, bit not constantly, I can pop to the loo. But I can't leave the secure area, as that requires a series of locked doors and waiting for hub staff to buzz me through different doors. So I can't get to my locker. So access to san pro is a problem.
In my area it is extremely restricted as to what items you can carry, so no, I can't wander around with a pocket full of tampons. And shifts are intended to be 13 hours, but regularly run over, so a tampon and a pad together is still not adequate.
I'm luck that the ward manager on my last ward job was a sensible woman and san pro was provided in the staff toilet. I doubt this cost much, but it really helped staff avoid having to have embarrassing conversations about being on their period and ask for accommodations to this each shift. And I imagine the low cost was worthwhile, as a happier and less stressed staff team has a benefit in less sickness and more productivity.
I'm not suggesting that providing san pro will solve every problem in nursing, but it is one problem that is easily solved.