there are many different reasons why someone forgets peoples names....

for some its because they drink alot of alcohol
for some its because they have or are doing drugs
for some its because they are on all kinds of medications
for some its normal
for some its a learning disability
for some its part of their mental disorders
for some its part of their physical health problems
for some its their diet or not getting enough sleep...
for some people its called brain strain (slang talk) for too much time on the computer, too much researching mental and physical health problems so what one is reading about becomes their own (medical and mental health college students get this one alot,too much of one thing causes other areas in a persons brain to shut down and stop storing that information because its deemed unimportant to what the student is needing to do at that moment)

my point only your own treatment providers will know why you dont remember people.

in me its part of my having bipolar disorder, MS (a physical health problem) and many other things too.

my suggestion if this continues to bother you contact your therapist or psychiatrist and they can tell you if your medications need changing, and any other treatment plans that can help you to have a better short term and long term memory (yes there really is medical and mental health treatments that help people with how their brain works and improving memory skills no matter what the cause is. )