Also worth considering post pandemic manufacturing in the Far East is in huge demand and even manufacturers like Surly have dramatically cut their range..
I'm sure we've had this conversation elsewhere...
A company the size of Surly will have made those model decisions long before the pandemic, a couple of them were even rumoured before. Even so, if you compare their current range with what they had say five years ago, I'd expect there to have been a similar number of models. I haven't counted, but it appears to me they've introduced as many as they've discontinued, what we're noticing is the overlap, in that the new models were introduced first.
As for the Mercury being discontinued, I'm a bit surprised, it must have been a good enough seller for it to have warranted the recent model update. I doubt many will consider the Audax as a suitable alternative, not least because it'll involve re-writing all the criticism of non specific frames Thorn have published over the years.