While it is absolutely true that there is a power and feature creep, what you didnt mention is that there is also a blizzard (and player) obsession with end game content and balance changes. As >>20664
said, instanced content became the norm, specifically expansion packs. While back in tbc and wrath they mostly existed to keep adding good ideas into the game, post-wrath saw xpacs become more about "release new continents every year to make players buy the endgame again so they arent left behind by all the other max level players". What's important to note is that world of warcraft is FULL of content. There's plenty of old raids that existed primarily for gold farming up until the gold drops were reduced in legion. There's plenty of old pvp zones like wintergrasp and tol'barad that are just collecting dust.
What blizzard SHOULD have done (and what i wouldve done) is ceased increasing the max level. Completely stopped it. Level 100 wouldve been a great stopping point. They also should have made all old end game content scale in level to be equal to new endgame content. Lastly, they should have allowed players to choose an expansion to play while leveling until they reached MAX (100) at which point they could experience ALL RAIDS and pvp zones from all expansions including classic in order to get max level gear and items.
Basically what im saying is that siege of orgrimmar wouldve been level 100. Ahn'qiraj wouldve been 100. Heart of fear 100. Tempest keep 100. black temple 100. All drops would be level 100 as well. This is possible with current technology using level and gear scaling.
As you reached level 60 you'd have the option to choose an expansion to experience. Everyone who chooses that expansion would share a server. The newest xpac would still be part of the game, so if you had trouble leveling youd have an option to do the newest xpac. This way people would still be motivated to do new content but without being forced to. Upon reaching max level you'd have access to any raids you wanted. This way people would be motivated to experience the storyline of each expansion pack and end game content would be filled to the brim with interesting raids. Call it "story mode" gameplay. As for how to farm gold without being able to solo raids the solution is agaiPost too long. Click here to view the full text.