I'm guessing you've never heard of the Mythic+ system, or the massive success it was in Legion, to the point of being considered one of the best features that had been introduced in that expansion.
First of all, a dungeon with scaling difficult would already be more accessible to players, due to the simple fact of requiring half as many players (4 instead of 8). Second, the content wouldn't be "much easier than Savage", since you wouldn't be getting the raid-level gear until higher difficulty levels, that's kind of the point of the whole scaling difficulty thing.
Short answer: Because players find it fun to progress in an MMO.Originally Posted by MoroMurasaki
Long answer: Because there's literally no other option of similar difficulty that allows players to obtain gear above the stuff that can be easily grinded for (ie: facerolling dungeons for tomestones, buying crafted gear, gear from Alliance raids). Mythic+ is seen as an alternative to raiding, without the hassle of organizing a group of 10-30 players. It allows players who prefer tight-knit groups, or prefer to have their playtime be much less schedule based (ie: hopping on to do a mythic+ or two) to still progress at a decent pace.
To answer your blunt question, because there's isn't any non-raid content at similar difficulty level, it's literally the only option people have. This is the raid-or-die mentality that I was talking about. Add actual options of similar difficulty (like WoW did), and I wouldn't be surprised for people to show interest in said options, despite having chosen to not do savage raids.
It's a direct reply to Ilan, specifically the part where they said "You basically want that you get raid gear outside of raids which is not right. If you want it put in the effort." as if people who don't raid are somehow incapable of putting in the effort of clearing difficult non-raid content.
But I agree with Ladon here. As we're reaching the fifth anniversary of ARR, it's becoming more and more apparent that SE isn't really all that interested in shaking things up, preferring the safe content cycle that they're currently working with.