OTOH, we can go through a huge list of NFL teams and ask why they would give up a 3rd/4th rounder to get a guy whose probably not better than the TEs already on their roster. You have to go through over half the NFL to find teams where Ertz is a significant upgrade at TE. And then we have to ignore the rebuilding teams who shouldn't give up draft capital to get a TE past his prime. At that point, we're left with maybe 4 or 5 teams that might want to give up a draft pick to get Ertz but I still doubt it would be a 3rd/4th.
How much better is Ertz than other free agent TEs this offseason?
BTW, I don't hate Ertz, and if I had him in fantasy, I might hold him too. But I wouldn't trade much to get him.