Can someone please ELI5 why ASICBOOST would be considered an exploit? Especially considering Satoshi clearly got caught off guard by the quick rise in GPU mini

Can someone please ELI5 why ASICBOOST would be considered an exploit? Especially considering Satoshi clearly got caught off guard by the quick rise in GPU mining-- which led to the bootstrapping mechanism putting Bitcoin in fewer hands than it otherwise would have. But I never saw Satoshi call GPU mining an exploit.