The engineering decisions are not based on beliefs. They are usually trade-offs. Safety in Rust has a very specific meaning clearly outlined in the official book. There are users who prefer it for certain tasks. The answer to your last question is also in the book.

Why not state it here in a few simple sentences, like for a 5 year old? Clarity is usually an evidence for deep understanding. I hope I will be able to get it.

Memory safety without garbage collection. (While still supporting dynamic allocation.)

Go is less safe due to the "Off to the Races" problem, but there's a legitimate debate as to whether that safety loss matters in practice.

Common Lisp and Golang use GC, which exacts a performance cost in some scenarios. Go also has highly dynamic semantics (e.g. with defer) which have unavoidable performance overhead, especially in an AOT compilation setting.