That's my experience as well - I had it 17 years ago, was very ill for weeks, but recovered and haven't had any problems since (but am no longer exposed to risk of new infections). However, it used to be that in the US you could donate blood if you had seen a doctor and been symptom-free for 3 years. It's now a lifetime ban. So perhaps there's new evidence it's not so simple?

Edit: Or there just aren't many donors who have had malaria, so they err on the side of safety.