Putin is ex boss of the FSB, hundreds of his opponents have met violent deaths, hundreds more are rotting in prison on trumped up charges, his St Petersburg mafia gangsters are in many of the most powerful positions, he is the richest man in history and the best protected. He thinks nothing of using a whole regiment to protect each of his many palaces.
However he has made a lot of enemies. And recently he has annoyed lots of the top people. Their fortunes have collapsed in value and they can't visit their South Kensington homes. Their Gulfstreams are gathering dust at Vnukovo.
Many think Putin has gone too far, that he is a loose cannon and his proclivity to escalate can only end one way. With Moscow becoming a glass car park.
To plan a coup against Putin would be incredibly dangerous for the plotters. So taking time to plan it in detail in advance would expose them to much danger. Better to just do it quickly, then do the planning afterwards. A slow motion coup.
This is one possible explanation for what has happened. Disappear Putin then take time to sort things.
If this were the case the sort of people who carried it out would not be any better than Putin as leaders. Just the usual authoritarian, kleptocratic gangsters.