Shadowlands is launching with fewer dungeons, zones, and less staple content compared to the past. In addition, there will be no new features, races, classes or professions with the expansion.
So the question becomes, where has all the saved development time by not adding these standard expansion features gone to instead? Usually those resources are devoted to expansion gimmicks like Artifacts, Warfronts, Garrisons or other things. But in Shadowlands' case, it has no new gimmicks yet STILL has less staple content.
There will be class reworks, but there are always major class reworks in every expansion, yet these expansions still manage to launch with new features like new classes on top of the reworks. So that is not an excuse either. And with the end game zone being barren with your typical reputation grind (Covenants), it makes you wonder what the questing and zone team have actually been doing with their time.
All in all, it seems like Shadowlands has thinned out the amount of staple expansion content that WoW typically provides, without actually giving anything in return. The only explanation I can think of is that a significant portion of the WoW development team has been moved to D4 (similar to how much of the D3 team moved to WoW in Legion). As a result of this cost cutting for WoW, there is less raw content in Shadowlands.