All games have a natural decay in the number of players that play them. Unless something fundamentally changes within the gameplay (a la FFXV or No Man’s Sky), it’s unlikely that an influx of players will happen unless it goes FTP. The face that EVE has maintained it’s account/player numbers is pretty impressive (see graph from EVE-offline below)
EVE has many things which discourage new players from joining and staying - The cutthroat nature - losing everything when you die, being scammed, being ganked etc. discourages people who like more casual games. like WoW. The biggest I think is the skill gap. This isn’t pay to win, but pay to compete. Of course lower SP characters can still participate in fleet fights, but without injecting they can never catch up with a player that started before them.
Multiboxing is not even close to being the biggest problem with player retention.