I feel like a big part of this is because the Disc isnāt just a fantasy world where they have condom factories, but a fantasy world where condom factories are actually relatively new. The inventor is (was) still alive, and his products are still somewhat controversial.
In most fantasy settings, The Magic Is Going Away basically means āthe world is going to be the same medieval cesspool itās always been, but now you wonāt even have a friendly neighbourhood wizard to cheer you upā. You donāt see that many fantasy settings that change beyond occasionally getting rid of the old āevilā ruler and bringing in a new āgoodā one.
Discworld, on the other hand, progresses. Over the course of the series (which appears to be only about a generation or two, in-universe) we basically see Ankh Morpork go from a Stereotypical Fantasy City to a Functioning Society.
We watch them develop newspapers, a police force, a postal service, what amounts to a telegraph system, and a railway network. We see dwarves, trolls, vampires ands goblins slowly gain acceptance. The Mended Drum goes from being baffled by the Discās First Tourist to holding choreographed bar fights.
And there are moments where people mourn this.
One of Cohen the Barbarianās main purposes as a character is arguably to mourn this shift from an old-style fantasy world to a society with real world implications. The short story āTroll Bridgeā, where he goes out to fight a troll and ends up reminiscing with him about The Good Old Days when heroes used to fight trolls, is a great example of this.
Angua worries about the melting pot only melting one way and erasing the cultures of fantasy creatures. The dwarves have a whole movement to try and preserve the Old Ways, even as their children embrace the New Ones.
In āShepherdās Crownā, right after we just had a whole book about how wonderful the railways are for the Disc, we have Tiffany Achingās father wondering if heāll be the last Aching to own a farm on the chalk (and have that familyās semi-magical connection to the land), because Wentworth would rather be an engine driver.
There are several moments throughout the series where characters do stop and look back at how things used to be, before everything went Modern, and feel some sadness about the things theyāve lost. But the series is also very clear about the things that are gained.
And thatās what I think makes it so realistic. Progress rarely does go all one way, and some things are always lost, but most people accept that you canāt spend your whole life pining after the elves (who were never really as nice as you remember them) when the city needs condoms.
