The thing about losing Tropeano is some of us have been following these guys closely. ...
I think the rest of what you're saying might be a tad colored by the above bias. Maybe people have forgotten this, because it's been a few years since the org was really trading prospects of any significance for Major League players, but, that's baseball. Lots and lots of prospects come through every system, and many of them become personal or sentimental favorites. Some of those will come up and stick with the big club for a while, and some will be used in trades.
You and a few others seem to be hung up on the Astros not thinking highly enough of Tropeano. Perhaps they did think pretty highly of him, but they also think highly of Conger too? And maybe they're wrong on that. It really depends on how you evaluate the different contributions of a catcher, and what you think Conger's true talent level is. And, of course, the Astros' relative near-MLB-ready pitching depth compared to their near-MLB-ready catching depth.
But basically every team that's not mired in a total fire-sale rebuild is going to make deals where they trade away prospects like Tropeano, on a fairly regular basis. And it doesn't always feel good to see those guys go.