I am guessing that a typical OTCBB company that is in the long steady process of going down the drain (as many OTCBB) could be on the Reg Sho list for a long time, as there is no need for the shorts to cover. No need for the SEC to devote resources to them (whether they should or not).
With an occasional exceptional company like SPNG that is actually going to go up, dangerous to be short. Shorts will be forced to cover at some point by margin calls, etc.
Anyone, correct me if I am wrong. Just a semi-educated guess.