Larian Studios Forums Baldur's Gate III Baldur's Gate III - Mega-threads and Guides The Turn-Based/Real Time with Pause topic

or the veterans would have complained about nostalgia milking.

Minsc showing up in the forest for no reason would have been even more jarring.
Also every single recurring charcter from BG2 must have quite a few levels under their belt so introducing them early in the game would obviously break the flow of the progression