Sci fi book about virtual reality where a race disappeared due to playing too much

Sounds a lot like the 1961 german novel Der Orchideenkäfig by author Herbert W. Franke, seems to have been published in English as well in 1973 as The Orchid Cage.

The plot goes like this:
A degenerate humankind lies most of the time in high tech fully automated beds and plays games. Those games are not VR but involve real robot-avatars. These avatars come into being by a projection of information onto other planets, first step being the creation of nanomachines in desert sand, which in turn create perfect human bodies to use as playing-avatars for the amusement of the humans on earth.

The story follows a group of young people playing a brutal game of battle royal on an unspecified alien planet, where the goal is to kill all others. Specific, very nice detail here: one of them cheats by dialing down the pain-reception of his avatar which is supposed to be foul sports.

The main protagonist of the story shows the rare treat of curiosity absent in all of his friends and chooses to explore ruins found on their chosen deep space playground planet. He finally gets to the core of the mystery by exploring large, empty, old, perfectly clean and functioning underground compounds run by machines. At the lowest level, completely shielded by the automatons, he finds a large room with myriads of plants. It turns out, they were former sentient beings in VR-devices which over time were fostered to death by the machines which took away bit by bit their bodies and gradually everything else presumed unnecessary to their wellbeing, leaving them like plants. The main protagonist´s avatar is treated in the same way, killing his avatar. He wakes up in horror in his fully automated VR bed on earth and smashes the device. He leaves his apartment, horrified by the implications of what he saw for the human race.