Simply because there is a horde of people playing diablo and there are no equipment sinks. This means that all the good equipments are staying in the economy, while the crap gets salvaged/sold to npc. Once that good gear becomes standard, a new harder to obtain gear becomes standard, and the tier of acceptable gear keeps getting pushed towards perfect drops which are extremely rare.
How to fix this??
Add more consistent drops. At the moment there is too many variables to make a gear acceptable. Not only do you have to roll the desirable stats but you also have to roll good values in those stats. It works out that it takes about 2100 gloves to roll your main stat + trifecta(assuming odds are equal) but actually getting high values makes it even more rare. So it would probably be more 10,000 gloves before you reach good trifecta glove.
Most armors are like this, depending on what type of armor depends on what the desired stats are and the values they need to roll to be deemed worthy.
What if instead we made the values of these rolls more consistent, lets say that items would always roll in the top 10% values. This would mean that people would find alot more desirable gears. Yes certain gears would still be extremely rare bc you need 4 or more high stats but over all i feel people would feel that farming actually yielded some decent drops.
Your saying flood the market with good gears?
No not at all, this is where upgrading comes into play. Add a moderate chance for equipment to break when upgrading. This would change BiS from finding that 1 in a million drop to being able to upgrade that item to a high tier.
This means players would see alot more desirable items drop and equipment would be leaving the economy rather quickly.
I was thinking something along the lines of upgrade lvl x1% to all atrributes on that item.
EG +4 would make that item 10% better, +10 would make that item 55% better
I can see a huge excess of demonic essence, so why not use that. I think a good cost would be 1xupgrade lvl. eg +4 would require 4 essence and +8 would require 8. You could also add fiery brimstones to later upgrades to make them slightly more challenging.
Up to +4 is safe, meaning that all gear can reach 10% bonus without breaking
+5-7 is a 50% success and 50% chance to break. This means only 1/8 armors will make +7
+8-9 should be like 20-30%. At 20% it would be about 1/200 making it to +9, at 30% 1/72 for +9
+10 should be 10%.
Less itemization and better loot rewards but they need to be upgraded to be worthwhile.