Segregation and the Civil Rights movement is still easily within living memory here, and people remain very sensitive of symbols from the time period that were used to make blacks appear simple and sub-human. Blacks as monkey imagery was (and still is in certain unsavory parts) popular amongst racists to taunt blacks for being “less evolved” and the association of blacks charicatured as monkeys with racists is strong enough that even if you’re legitimately trying to make fun of some other aspect of a black persons persona, people are going to assume that you’re aware of the racist overtones and that thats at least part of the idea your trying to communicate.
Its sorta like if you drew a charactature of Bernie Madoff with a comically long nose and have him hugging a bag of money. The guy does have a decent sized nose, and he certainly liked money, but its impossible not to read such a cartoon as anti-semetic simply because so many similar cartoons of Jews were used by anti-semites prior to WWII.