Assuming $40 per month for storage, that means one in three American households are paying for storage.
$40/month for storage? In the Northeast US, a 10x10, no climate control, is easily $150/month, and with climate control is more like $220/month.
Incidentally, I am friends with a couple who had 4 climate controlled storage units in the town they moved out of, some 6 hours away from their new place, so were paying over $1000/month for storage. They accumulated these over about 10 years. Four years after the move, they are now making periodic weekend trips back to unload/clean them out, and have made great progress, in only a year, they are down to 3 storage units! Just a few more years to go! So they are doing THEIR part towards the $22B, even if I'm ashamed to say I'm not. . . :)
I did suggest to them that they rent a house with one more bedroom, and put the stuff there, and it would be climate controlled and much cheaper, but apparently then getting rid of the stuff would be overwhelming, and they (well, she, the wife is a bit of a control freak) would never manage it.
And I can tell you it is a good business, I just had to arrange for transferring stuff where I work from a more distant to a closer, larger storage unit, and the place I was going into, which has probably 100 units in the building, says they have maybe half a dozen vacancies a year, with waiting lists for most of them. Ditto from another facility I evaluated, about a mile from the first one. Climate controlled is in particular demand.