Baldur's Gate III - Spoiler Edition (please read updated OP)

And yet he did give up, so this regret does not sound entirely sincere.



The logic here is not straightforward. For example, there is some powerful evil threatening the realm. While a hero cleric may rely on the corresponding good divine interference to help defeat this evil threat, a wizard does not have this type of backup. Mystra won't interfere directly or indirectly unless the balance of the weave itself is threatened. Mystra is just a power plant that imposes no limit on the power one can grab from the weave (on both sides) provided that it does not disturb the balance. Eventually it comes to whoever can grab more magical powers to defeat the opponent, be it on the good or bad side.

Of course, there is also Elminster to save the realm if everything else fails. While being Mystra's chosen, he acts largely on his own and possesses immense power. In BG3 he's just a messenger and does not particularly fancy the message he has to bring to Gale trying to clearly distance himself from the subject. Seems like Mystra considers Gale's mere existence as a major threat to overall balance and would prefer this threat eliminated on its own through Gale's voluntary sacrifice despite Elminster having his own opinion on the matters. It is a very well written plot arc IMO.