It was a deliberate design decision to limit the amount of storage in the game.
Also this from the 14th September stream:
"IMayBackstab: @CrateEntertainment any plans to assimilate some of these inventory/stash mods for a 5 or 10 dollar fee? Your players would be happy to spend that while also not splintering the player base as much with mods
I mean the people who have created these utilities for you guys have done them from their own free will for free and us basically taking that and charging money for it seems very unfair to them. And from our development perspective we have design decisions for why the bags are limited as they are. It is not just arbitrarily limited to screw you guys over, there are genuine reasons why that isn’t the case. But for those of you who want more stash space, that is why we allow modding and that is why you can use those utilities so you can have as much space as you want and because they work outside of the game they don’t splinter the player base. You can’t only play with people who use GDStash or GDIA, like you can play with everybody."
Stash tools overly complicated? I found both GDIA and GDStash easy to use and I’m certainly no computer tech wizard, just the opposite.
Honestly, this question has been asked so many times and the devs have made their position clear - infinite storage will not be happening. If you want that you’ll have to use a third party stash tool.