I never heard of this the first time round either! The "set in the North" excuse isn't really valid, lots of other shows have been, and got good viewing figures.
Going back a bit, Likely Lads and Summer Wine (that one a mere 37 series?!!) were pretty northern, as were 'Bread' and 'Cold Feet'?! What else, er, Happy Valley, Scott & Bailey, Last Tango in Halifax, pretty 'northern', and Downton Abbey was set in the north, albeit generally filmed further south, and got stellar viewing figures!
There are lots of reasons for shows getting cancelled, not just viewing figures, but this show averaged about 2.5 million. That may suggest that though commenters on here liked it, the broad appeal wasn't there? Van der Valk in its revamped guise (2020 to 2023 so far) was getting over 7 million viewers for example.