Compatible I2S source devices

Paul McGowan said I2S is better than UDSB, certainly, but I do not know if those interfaces you mention will work.
Other than there being relatively few compatible I2S sources, is there any reason why one would not want to strive to use I2S if possible? Since I2S is essentially the native format for DACs, doesn't I2S simplify the process by eliminating extra digital conversion steps and eliminate the numerous potential issues with USB? I am trying to understand why I2S is not the clear way to go.