There are models of GPUs with AIOs, EVGA makes their Hydro series, Gigabyte has their waterforce series. They just usually aren't worth the cost since you have to design a new full cover block not just got every generation but also usually for different cards in the same gen too.
Lastly, TDP is not a defined standard and each manufacturer defines it differently. Intel for example defines TDP as the maximum allowable power draw under full load. How that translates to actual heat output depends on architecture and process node. Intel's most recent chips for example all max out at just over 100 watts TDP, but they're known to need 200+ watts of heat dissipation for sustained workloads.