Speaking to Express, Hirst explained that the reason why Rollo was left out of the series finale (and season 6 in general) is that his storyline had already finished in his saga, he had already been established as the ruler of Normandy, and was no longer part of the series' narrative.

Why did Ragnar leave Rollo behind?

When the Vikings return, he successfully propels them away and out of Paris. Ragnar knew what his brother was capable of because he'd experienced it before. The only reason Rollo was left in Paris is because Ragnar was too sick and wasn't able to make the deciding factor sooner.

Did Rollo betray Ragnar in real life?

While Rollo ended up playing a significant role in Vikings, some fans may not realize that he also had a big part in real life too. ... He manipulates, backstabs, and betrays his brother Ragnar and his fellow Vikings.