All good reasons and possible any of them could be correct or a mix of them. I think as others have said that part of it is how well some of these fish could do or would do if released even in colder waters. Another aspect that
Jexnell
touched on is the laws pertaining to catching and keeping fish. Some you can catch and release only others you can keep but only to eat you can't house it as a pet. Weird laws. I really like perch I think they are cool looking and what about a musky instead of the arapaima?