Take a look at the FDIC's
FIL-81-2010. "Final Overdraft Payment Supervisory Guidance," and the
FAQ issued in April 2011 concerning that Guidance. That's where you will find the "expectation" of the FDIC that is described as "meaningful and effective follow-up" to excessive overdrafts, and it's probably the genesis of your bank's procedures.
There is always the choice to close out accounts like the ones you describe. Lots of banks take that path, perhaps to avoid regulator criticism. Other banks leave the accounts open, usually keeping an eye on them to avoid losses -- to the bank -- perhaps feeling that if the customer appears not to care how much money they lose in fees, it's not the bank's problem (not to mention it's a big chunk of income -- especially in the low rate, no spread times we are in -- for the bank.
I live in a summer resort area, and worked at a bank here for over 30 years. We had one branch manager who regularly let several summer businesses' accounts run overdrawn for much of the summer season, each business making deposits periodically enough to cover those overdrafts, albeit after they had been overdrawn for several days. One Labor Day weekend, we had a major storm, and the tourists pulled up and headed home the Thursday before. The town where the bank branch was located seemed as desolate as in mid-winter, and lots of businesses had a miserable weekend saleswise. A couple of those chronically overdraft businesses closed up for the season, leaving their negative balances in the dust. The mood was grim at the next managers' meeting, to say the least. Overdrafts were managed differently thereafter.