Probably because
'monkey' and 'ape' haven't really been used as terms of racist abuse towards white people. Not that I think this image is racist, but I think you have to be careful when doing stuff like this, mainly because you can never be 100% sure how the audience will take it.
It's a bit like when people say, 'Paki isn't a racist term, it's just a contraction of Pakistani.' Maybe it is and maybe it isn't, but your opinion on the meaning of the word might be coloured had you ever had 'Pakis go home' spray-painted on your house, or had it shouted at you in the street.
( ,
Mon 30 Nov 2009, 12:51,
archived)
It's a bit like when people say, 'Paki isn't a racist term, it's just a contraction of Pakistani.' Maybe it is and maybe it isn't, but your opinion on the meaning of the word might be coloured had you ever had 'Pakis go home' spray-painted on your house, or had it shouted at you in the street.