Great article in the Athletic about the Canucks losing out on OEL, Markstrom and Tanev, and then eventually getting Schmidt to fall into their laps (while losing Stetcher and eventually Toffoli along the way):
https://theathletic.com/2138908/2020...at-comes-next/
Basically, with Pietrangelo pending to Vegas, Schmidt wasn't shopped around the league but instead was offered to the Canucks for a mid-round pick if they were able to take his entire contract. Benning agreed but had to sit tight until the Pietrangelo deal was official; he reportedly asked Stetcher to wait for them (as he needed to keep cap space open for Schmidt) but Stetcher ended up signing with Detroit instead (it was reported that Tanev and Stetcher felt "spurned" by the lack of communication from the Canucks).
I also read about at theory (elsewhere) that Schmidt agreed not to have a full NTC on the understanding that Vegas wouldn't trade him, so that might explain why Vegas didn't shop him and instead approached Vancouver specifically (i.e. assuming that is where Schmidt was willing to go).