Here's an interesting factoid about why Metallica chose to play that certain deeper cut when they were playing your town: a lot of people probably listen to that track on Spotify.
At least, that's what Spotify CEO Daniel Ek said today on a conference call, according to a report by Quartz:
"You have an artist like Metallica, who changes their setlist on a city-by-city basis just by looking at Spotify data to see, which the most popular songs happened to be in that city. We've never before been at a place in time where you could make as many informed decisions and understand your audience as well as we can do now as an artist."
It's actually a pretty smart move. More bands with a deep enough catalog should take this analytical approach.
Blabbermouth noted that Lars Ulrich spoke in a 2017 interview with 98 Rock about how he typically choses the setlists:
"I'll sit and look at last couple times we played [in the area] — whatever city we're in, I'll look at the last 10 years worth of shows from that particular city. Obviously, there's certain songs we 'have' to play, but then there's the deeper cuts — and the deeper cuts I always try to vary. So if we played 'Harvester Of Sorrow' the last time, maybe I'll put 'Through The Never' or 'Breadfan' or whatever. I try to vary six or eight of the deeper songs so you give fans a different setlist and a different experience. Since I started doing that, it correlates with when we started taping all our shows and we offer them for sale on something called LiveMetallica.com, mixed by the same team that mixes our albums. Since we started doing that in '03 or '04, we haven't played the same setlist twice."
"It's not just for the fans, but it's also for us — it keeps us on our toes."
"[Back in the day], we were out doing the same setlist for weeks at a time, and I was telling the lighting director, 'I'm gonna change a couple songs in the setlist tonight.' And I remember he said, 'Give me a 3-day notice so I can program the lighting rig.' It was one of those moments where I was, like, 'Wait a minute! That's what it's come to? If we want to play a different song in the setlist, we have to give the lighting guy a three-days notice so he can change the green lights to purple lights? That's not rock 'n' roll.' If I want to play 'Sanitarium', I don't want to have to hire an electrician. [Laughs] It was one of those moments: 'Holy fuck, I don't want to be that kind of band.'"