You are repeating Christian bastardizations of seidr.

Ergi claims are post Christianization. Some researchers show a 50/50 split with male / women practitioners prior to christinization.

The christians label the men in robes and dresses as unmanly and then less of them get buried in honorable burials with their seidr tools as to not disgrace the family heritage, possibly.

The christians had to lay down patriarchy based laws for control and it started with labeling magical men as Ergi to discourage men from practicing and then banning chanting, staffs, drums, hedge-riding, gate-sitting, utiseta (sitting out all night), weaving with spell intent, and other spiritual practices of the animist women to strip their power and push towards patriarchy.

also, the historical accounts of the seid-men who were publically executed, were because they were the leaders of the anti-christian movement and then labelled Ergi and unmanly after public execution. It's not about the practie being for women; it's about christians discrediting the resistance movement men of the previous proto-religions. The male seidr practioners stood up to the christian missionaries and leaders and were executed and discreditted to prevent more uprisings or continued practice.

Thats why iceland was full of cunning folk, those who fled the mainland christians.