The problem is that when ammo is available, there's no reason to not buy as much as you can so you don't have to keep going through the hassle.
For example, I purchased 400rds of 308 (Could have bought 4000), although that's enough to last me a year or so. I don't need it right now, but it was available at a decent price, why buy again later.
Same with components like primers. 10,000 small pistol primers will last us a year, so I don't need them all right now, but why go through the hassle later?
The problem exacerbates itself, since it's not worth going through the hassle so people buy more than they need at the time. I'm able to check websites and get notifications frequently, so I'm able to find just about anything within a week or two, but other people don't have that kind of flexibility.
Not to mention the other unlicensed individuals who are buying bulk and reselling locally for 100%+ margin. Would love to get a copy of their ID and submit to local and federal tax authorities...