Good players almost never get released in season in the NFL barring off field issues, locker room problems etc. Ertz has been an injury plagued non entity for almost 2 years and Cook looks washed. They might be more recognizable names than your average street free agent or practice squad guy (practice squad guys like Julio Jones and Leonard Fournette?) but this isn’t like some team picking up a Dugger or Onwenu dumped by his team in a contract year or something.
I don’t see what problem is being solved by freezing rosters or limiting who can sign where. Trade deadlines and roster freezes are to prevent bad non contender teams from dumping good players to playoff teams. Since most good NFL players (the guys you’d worry about providing some sort of competitive imbalance or collusion) come with dead money salary cap hits for the next season, teams are disinclined from just cutting guys in-season who aren’t in their future plans.
Kickers, long snappers and punters are a good example why any sort of roster freeze doesn’t work. There’s barely 32 (and that’s a stretch) guys who can do those jobs at an NFL level but they don’t get hurt often. There certainly aren’t 64 NFL caliber or even close to it guys out there in any given year. Probably not even 45 of them. You’re not going to have teams waste practice squad guys on some kicker twice as bad as Ryland or some long snapper who didn’t even get a training camp invite. What happens when those guys get hurt? You call up the 33rd or 38th or whatever best guy and pull him in off the street. And, as we saw with the famous story of the Patriots, sometimes you pull a guy out of his classroom to long snap for you in the playoffs because the 38th best guy just went down with an injury.