You are missing one other issue: it seems easier than it really is. There are only so many people who would use self storage. You see a full self storage place in town and thing you can get a share if you just build one. What you don't understand is demand is not elastic: if you build a second site in town you go from 100 units with 90 used (a good usage rate), do 200 units in town but still only 90 used.

Eventually price crashes far enough below retail that commercial users start filling out a lot of the space because the cost per square foot is lower than their own space.

Like you shove your winter PPE, your emergency stash of spare parts for process equipment, etc, etc, in some self storage lockers and get the same job done using less square footage with extensive compliance burden (or get more job done using same square footage).