The practice squad generally has two purposes. The first is to stash a few guys who are basically backups on demand. These guys are ready to fill in as back of the roster guys on an as-needed basis, and ready to be a temporary stopgap for limited playing time in the event a rash of injuries hits. Generally speaking such practice squad guys are a bit more experienced, in their second or third year in the NFL, and may have somewhat limited upside. Though the practice squad does not prevent such backups to the backups from being signed by other teams, if any other team signs your practice squad guy they have to either put him on their 53 man roster or pay him as if he were on their 53 man roster for a minimum of three weeks. This provides enough protection as to make poaching of other teams' practice squads a somewhat rare event, and provides a certain amount of stability at the level of emergency replacement guys.
The other purpose is to hold onto guys with much more upside but who aren't nearly ready to actually get NFL snaps. These types of guys are not counted on to ever be promoted in the current year, but are stashed to try and develop them for the future. Generally these guys consist of players with some outstanding physical trait(s), but who have to be developed extensively. These are lottery tickets; a few may pan out big, like Damon Harrison, while most will completely wash out. These guys are generally rookies who flash in training camp.
Then we have Dexter McDougle. Now in his third year, the idea of upside is fast becoming obsolete. Vanishingly few players ever spend their third year in the NFL on a practice squad and end up being significant contributors to a 53 man roster. Dexter doesn't really qualify as the high upside developmental project any more. On the other hand, he has been on the practice squad all year. McDougle remains there today, even while the Jets field arguably the worst secondary in the NFL. Even while the Jets have signed a cornerback cut by another team (Daryl Roberts) and a converted college quarterback from another team's practice squad (Nick Marshall) to the 53 man roster. If Dexter McDougle can't make the 53 man roster of the team with the worst pass defense in football, and he is being passed over multiple times in favor of guys who can't make other teams, one has to ask, why is Dexter still here? He apparently isn't a backup to the backups kind of guy. In his third year he is pretty clearly not a high upside developmental project any more. So why is he here?
In the hierarchy of what ails the Jets Dexter McDougle ranks pretty darn low. No practice squad player plays any significant role in what ails this team, and keeping a guy on the practice squad is hardly the most egregious mistake being made in Jets land these days. Still, you can question the process. There appears to be no justification for Dexter McDougle to still be here, yet he remains. It is clear from their actions the Jets have zero confidence in Dexter's ability to function adequately on an NFL level. If they don't trust him in his third year, why keep him around? Why not use that practice squad slot on some other developmental lottery ticket who, while unlikely, might actually pay off some day?
It is a small thing, almost too small to mention. But it speaks to a larger decision making process. It may be a hint that this front office is simply not too sharp in their decision making. To be sure, there are much larger issues. But sometimes the smallest details are revealing in the flaws they reveal if one is only interested enough to inspect the fine details of the organization. Sometimes poor results are the unlucky residue of good process, and sometimes poor process signals bad things ahead even if the poor process has little effect on the present situation.