But people have different ideas about what's fun in these games.
It's not like the game is changing or anything, closing a rift and then going into another one is still keeping the pace of killing extremely high. And regardless of what build you are going for, a top tier one or not, Kadala is still a better way to get items for it.
But anyway that is beside the point, the reality is in a game with so many difficulties only a few builds rise to the very top AND most people playing the game want to reach those difficulties. People wouldn't ask for build advice every other post if this wasn't the case. Without relying on Kadala you are going to hit a wall that takes a long time to overcome. I speak of this from personal experience. The drop rate of set items used to be way lower on the PC version and you could not get them from Kadala. Obtaining the 3 pieces of my Earthquake set took me quite literally around 300 hours, yes, about 100 hours of playing for each piece.
Most people never made it that far in the PC version. They got burned out way before that because they felt like they were making no progress on their character. You just get bored at some point pretty much. It almost happened to me as well, I was playing a lot less in those last couple of weeks before I finished my set.
must... get... more... shards!
Pretty much, Kadala is the only way to target most legendaries and you will be spending a lot of shards to get those items. I have personally spent 130k shards total (not including my seasonal shards which has already reached 10k). Basically my point is... you are going to be spending a shit load of shards to get all the items you want (without using console save cheats I guess). Just before I logged off a few minutes ago I actually spent 500 shards on chest armor and got 0 legendaries... It's just a thing you get used to.
Drops are still an important part of the game, but, it's just all RNG, you never know what you are going to get. It's mostly just like I said, the higher you go up in difficulties the more you are going to want specific pieces of gear, which Kadala allows you to get since you can gamble for any slot.