The question is more on the lines of, "Why did Navalny sleepwalk to his own death?". It was quite evident that Russian authorities would arrest him upon his entry into the country. What this action intended to achieve completely deludes me. Countries like Russia, which are spread across timezones and have varying temperatures and coastlines, were always going to pose a challenge to a Navalny-styled revolution. Of course, revolutions have happened in Russia before, almost a lifetime ago. When the government controls most of the media and even social spaces, achieving the change he intended necessitates a level of collaboration that is next to impossible. For this reason, just like Chinese dissidents, Navalny would have served his nation a lot better by operating from a safe country and returning only when he felt safe.