Because like Telles helped Shaw kick on, Trippier can do the same for Wan-Bissaka as he faltered a bit during the last stage of last season. Plus, his attacking game needs work. Trippier is a really solid, attacking RB. Dalot is a similar age to AWB and needs to play. Aaron will stunt Dalot's development and so I imagine he'd rather be a starter at another club. Plus, Dalot and AWB are a similar age and they won't really be learning much off each other. Besides, Dalot is an attacking RB, but isn't as good as Trips.