When developers lacked ideas for new content, they simply prolong the grind and therefore increase the waste of time of players in this game dramatically.
This is exactly what happened with the start of season 6. A few details:
Shortage of materials
Blizzard has changed the materials droprate to the point that players need to spend much more time farming materials. The shortage of rawhide was only one example.
Severely lowered drop rates of mythic uniques
While in season 5 the drop chance of mythic uniques was about 7 % for all bosses, it is now 2% for Duriel and Andariel and 1% for other bosses.
Severely lowered drop rates of ancestral items with greater affixes
The drop rate of legendary ancestral items with greater affixes was severely lowered in season 6, compared to season 5. Especially those with 2 and 3 drop way less often now than in season 6.
Severely lowered drop rates of maxrolled legendary aspects
Since maxrolled legendary aspects can only be on ancestral legendary items and since ancestral items only make a fraction of legendary item drops and since (on top of that) the drop rate on ancestral legendary items was severely lowered, you can play like 200 hours and you will have less than 25% of aspects with maxroll in your codex of power. It will take probably thousands of hours to complete the codex of power.
Introduction of RNG to Glyph Leveling
Compared to season 5, it will now take much more time to max all your glyphs. The reason is that Blizzard introduced RNG to glyph leveling, thus the chance that a glyph leveling attempt fails. This adds to already a lot of RNG factors in the game, such as Tempering, Enchanting and Masterworking, that all can fail and/or not produce the desired result.
New leveling system
It now takes way, way more time to level your char to the max level, with the introduced new paragon level progression.
All these things together slow down progress of players artificially without adding exciting new content to the game. On the contrary, it rather adds frustration to players, especially when it comes to items and itemization.
At the same time heavily demanded quality of life upgrades in the game, such as loot filter and ingame auction house, that could accelerate progression, are still rejected by the developers. Therefore players still have to regularly portal back to town to manually salvage the 99% useless items into materials which interrupts the game flow. Doing this hundreds of times leads to hours wasted only for salvaging items in town.
There is nothing exciting about all these things that lead to artificially prolonged progression without actually adding new exciting content to the game.