Storage is actually kind of a personal thing, in terms of what is the right amount for people. Some people obviously want infinite storage and wish they could collect and categorize everything in the game. Other people will never hang on to enough stuff to fill up the storage available. Another group likes to collect things but wants some limit that eventually forces decisions about what to keep and what to sell.
Both the second and third type of player are similar, just one makes the decision proactively to sell things before they accumulate and the other holds onto things for a while until they’re pushed into making a decision as space becomes limited.
If you’re a hoarder who wants infinite space, you might be thinking “why on earth would anyone not want to keep all their items?!” Basically because people start to become overwhelmed by the amount of crap that they have. It becomes tiring looking at it all, sifting through it, trying to organize it. Some people love that but most people find it burdensome. Yet, left to their own devices with infinite space, a lot of people would just keep collecting things to the point that they didn’t even want to open their stash and have to deal with all the shit in their there.
I think for many, myself included, it also starts to diminish the perceived value of items as you amass a vast trove of them. If you have limited space and you find a duplicate epic weapon, you’ll tend to look at the stats and sell the lesser one. With infinite space, you’d probably keep collecting duplicates, because why not, and you’d end up with a dozen pairs of “The Final March.” Personally, I’d find that kind of immersion breaking looking at pages of multiple “unique” items. I mean, sure, we all know that items can drop infinitely but actually collecting them and seeing multiple copies laid out next to one another for different epics just kind of twists the knife in the gut of my suspension of disbelief.
I don’t have any hard metrics on this but my feeling is that the majority of players fall into the categories of not caring about stash size, wanting a limit on it or not realizing they want a limit on it but would have a detrimental experience if there weren’t one.
Either way, it is almost a certainty that someone will create a GDVault type program to add infinite storage for those who desire it - in fact, I know people have already worked on one. So it seems most practical to build in some reasonable limit, not too small and not too large, that will please most players, then let modding take care of those who need to collect it all.