I was a mage with summoned bags in EQ. Those were the devil. Lost my jboots in those once. I did petition that, but got back a message from a gm that it was my fault, they would not get them back (which was the right thing to do, it was my mistake). Lost a godly amount of, forgot the name, the bricks you got in that ice dungeon with the spiders. Velketor? They were heavy and encumbered you without the bags that removed weight. I forgot to empty those so many times... EDIT: For those that did not play EQ, summoned bags would vanish with all items inside them once you logged off for more than 15 minutes. /end edit
The reason bags are used in most games is because they are an easy implementation of a feeling of item based progression that causes little to no change on the dynamics of the game. I like that there are many slots in my character sheet to upgrade. However, each one that can fit an item with stats will change the power of the player, meaning you need to scale the world after it. This is the reason (I think, without being a developer), that games avoid having 10 ring slots even though we could easily fit it with 10 fingers. In fact, it is unrealistic to only have 2 slots. If jewelry gave us stat boosts in real life, we would all look like rappers. But adding 8 more slots in a game would create a player with far more power, so the game would have to be balanced around that. Much easier to limit it to two. Increasing the amount you can carry with new and more bags will give you no power, but still adds an element of progression.
I doubt bag progression, for lack of a better term, is going away any time soon. But, I am not sure I mind that aspect. Inventory management is such a large part of RPGs, it would feel odd to play one without it. Weight restrictions is one of the first things I remove in games like The Witcher and Skyrim, but for a game like EQ, the removal of that would change entire classes.