I don't think it's fair to say that people simply aren't bothering in a way that implies they don't care. Even if people don't have a phobia, it can be a deeply unpleasant experience for many.
I have given blood a few times. Only once have they been able to collect the full amount of blood because I bleed too slowly apparently. But knowing that my blood isn't actually going to directly help anyone puts me off going through what is to me, quite a horrible process. I know that use it for other stuff, but other stuff doesn't give quite the same incentive. Especially when you know you are going to spend the nest hour or two feeling stoned and you have things to do. That's just the way it has always affected me.
Even so, I have been back to donate, and then turned away because I sniffed. Literally, just sniffed. I had the most minor of minor colds about a week before, and couldn't donate because of it. Obviously I don't want them taking blood they won't use, but again, it doesn't do much for making you want to go when you waste an hour waiting for nothing.
One time I went, I noticed a laminated piece of paper that said I could request anesthetic cream for when the needle went in. I had never seen this before. I asked if I could have it, and the nurse very much tried to put me off it. When I insisted, you would have thought I had asked for a golden bed and silk sheets to lie on with the fuss it created.
Still I went back, determined to do my bit. Then I got a different job and was unable to go to the sessions at the three centres closest to me because they all start at 12.00pm. I work in the afternoons, but could go any morning. They finish at 7.00, but I have picked my dc up from school by then and they usually have things to do that I need to be around for. DH isn't home until then, and he would have to leave work two hours early in order to have dinner before donating before they shut. So I haven't donated in over a year now, and dh won't because we need the money he earns as long as he is at work.
They really don't make it easy to donate, even for people that really want to.