No need to guess at why he did it; Navalny explained exactly why he went back literally in the first minute of his Putin’s Palace video, which he specifically timed to release on the same day he arrived back in Russia.

Hi, it’s Navalny. We came up with this investigation when I was in intensive care, but we immediately agreed that we would release it when I returned home, to Russia, to Moscow, because we do not want the main character of this film to think that we are afraid of him and that I will tell about his worst secret while abroad. One of these viewers is the most devoted admirer of our work, on whose orders I was poisoned, is Vladimir Putin. He is definitely watching this now, and his heart is filling with nostalgia. This is not only an investigation, but also, in a sense, a psychological portrait.

That portion of the transcript comes right after the silent opening text where protests are announced that coincide with his return to Moscow and guaranteed arrest.

Why can’t you believe what Navalny said himself? Or are you just sealioning?

Also, for anyone who hasn’t seen it, the video is excellent and the same information is presented on his text site (it is in Russian; use Google Translate or another translator to get the English version): https://palace.navalny.com/