You're speaking in terms of what you WANT to see. I'm speaking in terms of what we're LIKELY to see. In his press conference today, Stearns said they're planning on bringing back the "core" and going for the playoffs again. Burnes, along with Woodruff, are the centerpiece of that core, and trading any one of them is likely to severely diminish our playoff chances. Also, he talked about how he learned from the Hader trade how major roster shakeups can hamper team chemistry. All of which tells me that Burnes is highly unlikely to be traded this offseason, despite the massive haul we could get for him. More likely, he'll be traded next offseason if/when efforts to extend him have failed, and we'll still get a heck of a lot for him.
Same thing with Renfroe. A contending team cannot afford to trade him and rely mostly on rookies to step into his shoes, especially considering Renfroe was the best hitter on an otherwise offensive-starved team this year. If they trade Burnes AND Renfroe, as you want them to do, then they're essentially punting on next season, which would conflict with their stated desire to seriously contend.
Also, Renfroe is not "standing in the way" of the AAA outfielders being able to develop in the majors. If anyone was standing in their way, it was McCutchen, and he'll be gone next season. Meanwhile, Mitchell has already started his development and was a fixture in the lineup at the end of the season. Frelick is likely to see major playing time starting early next season (if not by opening day) as one of the other featured outfielders, with Yelich seeing increased time at DH. As for Ruiz and Wiemer, they'll likely start next season in AAA as they're not quite ready. And even then, Ruiz is probably best used in a utility role. They also could be traded to upgrade other areas of the roster, like for a Danny Jansen. Bottom line is Renfroe provides much needed offensive assurance for a contending ballclub, and his production warrants the $11 mil. salary.