Why wasn't it a problem until now, considering they've been perfectly fine since the 70s? If they were truly problematic, wouldn't they have gotten pulled much earlier? Seems like a complete overreaction to me, especially since Seuss wasn't trying to spread bigotry whatsoever.
Seuss was known for racial caricature and supported japanese internment. The Mullberry street that got pulled had a pretty racist caricature of a chinese person with the caption "chinaman"