Solo trekking, without a guide or companions, is never recommended.
This is nonsense. It's not for LP to judge what is acceptable risk for anyone. Of course it is advisable to have decent gear, knowledge etc. But the word is 'advisable' , people take responsibility for their own actions in the mountains.
Solo trekkers are often particularly careful because they are on their own. More inclined to listen to local advice and more likely to be carrying gear that could save their life in a bad weather situation. Groups of trekkers can be less careful if they have false confidence in the collective abilities of the group. It's questionable whether a group of inexperienced and poorly equipped trekkers are safer than an experienced, well equipped individual.