Lamb & mutton aren’t very popular in the US. In my experience, people who are used to beef expect lamb to be more or less like beef—and since beef definitely should not taste like lamb, they end up thinking lamb has an “off” taste and dismiss it without letting it stand on its own merits.

Thankfully here around San Francisco there are some butchers where you can source good lamb, and the ethnic cuisines include enough lamb that local Westerners are perhaps a bit more accustomed to it.