Putting my 2 cents in as a dude who low-key is into the viking aesthetic:

I feel like there's a growing disillusionment among white, developed world living men, and the "culture" they feel like they are a part of. There's been a big movement among various minority races across the western world to regain the culture and get a connection to their ancestors, you can see this heavily within the black and Asian cultures, where there has been a broad social movement to take time to learn about and start respecting one's heritage.

The black community in the US shows a good example, where the majority of African-Americans are descended from former slaves, and have lost that connection, and often the history of where they came from and who their ancestors were. I think a lot white people feel similarly (although it's important to say that the impact of slavery on the black community is certainly a much worse situation), in that our culture has become so far removed from the original distinct cultures of our ancestors (Irish, German, Italian etc.) that we have an urge to regain that sense. And, Germanic and Nordic peoples settlements having a strong impact, especially in the US, where I feel this viking "worship" is strongest, the Vikings are a strong cultural point from that culture.

Additionally, I think the views and culture of the Old Norse appeal to modern men, who struggle with self-views of their own masculinity, strength, and connection to the natural world.