Because atm they are underwhelming and un-fun. Complained in 1 about that as well. Saying this after a complete playthrough. DnD spells (in any DnD game up to now) were impactful - they felt powerful. PoE spells (except the best spell in the game- chill fog), even with a large amount of perception and accuracy, are unreliable and not worth casting except for crowd control in some situations. See much better results with non-wizards in my party.
And the new grimoire/spell system is not intuitive at all. Every grimoire has assortments of spells that I don't like tbh and re-training seems a must for every wizard. With these spell/element resistances in the game, if wizards can not versatile, they end up being useless in half of the fights. Why not let us write our own grimoire and use that as a gold sink as well?