It's not an issue. Those variations add game scope at very little resource cost. They're better to have than not have. For example, Barcelona GP is the layout that Formula 1, its support races, the 24 hours of Barcelona and most (if not all) automobile track days use at that venue. To properly replicate any of those races/events, you need the GP layout. The Moto layout is a better drive, so it's great that Kunos included it as well, but it could not be the only layout. Barcelona might as well be a fantasy track if you're only going to include the version that automobiles never use.
RE Nurb's layouts: most of the Nuburgring's many layouts are actually used in motorport or for other driving purposes. Nordscheife is the layout OEMs test/set times on, Tourist is the layout that's open to the public for driving, Endurance Cup is the VLN layout, Endurance is the 24H layout, GP is the F1 layout, GT is the BES layout and Sprint is the DTM/ADAC GT/ADAC TCR/BSS layout. Sprint GT is the only layout that isn't used (afaik), but why not have it as well? Some people might prefer driving/racing on that one.
That's the thing, more layouts add more breadth to the game and more options for the player. Some versions might be better suited for driving (for some, maybe not for others), some versions might be better suited for racing. Shorter/tighter versions might be more appropriate for racing slower cars, longer/faster versions might be more appropriate for racing faster cars. Some versions might be better suited for some leagues, others might be better for others.
I'm displeased as it is that Kunos eschewed Silverstone Stowe, Zandvoort Club and Barcelona Short, as the game needs all the track locations AND layouts that it can get.