From a third-party perspective this just looks petty. The players who refuse to renew did nothing wrong. Imagine if we wanted someone for free, how do we feel about another club banishing that player to the stands just because he doesn't want to renew?
There is some (albeit slim) chance he renews, when he (and his agent) see -after months of inactivity - he can only get the same money as here elsewhere.
That's the only possible positive gain for Barca following that strategy.
But, other than that, it's not at all how you describe it above.
You miss an important parameter:
It's not that club and player were negotiating, could not find a solution, and then they agreed to part ways.
Many such cases, Thiago and Alaba at Bayern, or Mbape this summer at PSG, where the players
respected their clubs despite wanting to go.
What happened is that the players left (or are about to leave) or run their contracts down
under the conditions of their clubs (they decided to either use them on the pitch for the remainder of their contracts or sell them).
Here, on the contrary, Barca wants to sell if the player doesn't renew. They do NOT want him to stay and run down his contract.
But the player and his agent want to do their own thing, play around, run down the contract against the decision of the club.
That can't be!
Stupid Moriba tried the same in the summer, and lost.
Alaba Thiago and co mentioned above never 'played around' with their clubs, trying to do their own thing while disrespecting and ignoring their will
PS: I wouldn't call it 'petty' at all. I would call it only FAIR (and mind you I love Dembouz as a player)