You may perhaps see now why so many of us can't believe how badly they handled him. The team has completely failed in evaluating their own player.
What's worse, they made their evaluation known to the entire world. The NHL is a perception-driven league fighting tooth and nail to avoid giving into assessment via measured results. Frost's measurable defensive results for a long time now are good. But the team doesn't "feel" like he's good because he isn't grinding enough or some shit. Hell, the fact that his defensive acumen reduces his need to block shots probably actively works against him.
So a team that was never going to use measurements of his results to drive up his value and instead rely entirely on perception, has spent years completely ruining the perception of Frost as a player by telling everyone who would listen that they (falsely) believed him to be bad defensively. Which made it inevitable that another team who knew what they were looking at was going to come in and lowball the unholy wet dung out of this management group.
It was from start to finish the Flyers' magnum opus in wretched development, handling, and PR around a player.