The sets they were using for the control room specifically was a very accurate reproduction of the actual Chernobyl control room. Compare: Series vs reality in 1977 (different angle)

I can't speak for all of them, but a lot of western nuclear plants wouldn't have critical functions in the control room on computers. Here's Forsmark NPP's control room, present day. That plant is newer than Chernobyl (online 1980) Note the panels with the analogue meters in the background. When I last was in that room (summer job in 1997) there weren't half as many computer panels, and the computer systems were not handling critical functions. Here's a picture of the Forsmark 1 room at opening; all those "50s" panels, in a newer, western reactor. Here's the Barsebäck (a Swedish, Chernobyl-contemporary plant) control room on its closing in 2005 (which is more like Forsmark at the time I was there in terms of the number of monitors) - Like the Chernobyl picture from 1977 there are a few monitors but the main panels are all analog. And yes, those aren't that different from how it'd look in the 1950s (e.g. at Ågesta NPP)

The reason is that nuclear power stations were not built to use the latest and greatest digital technology to control everything. There's simply more that can go wrong, and it did not necessarily have predictable modes of failure, which is an important safety concern. It's possible to visibly inspect a relay if it is open or closed, it is possible to build them so that they're most likely to fail in a certain (on or off) position. Neither of those thing are true of transistors. (which is not to say analog control systems and mechanical equipment don't have issues as well) Certainly Chernobyl had computers in offices and such, but not critical monitoring or controlling the reactor - because neither did anyone else's reactor at the time.

Switching to digital control systems is something that began in the 90s and is an ongoing process. The first 'all digital' reactor went online as recently as two months ago.