I don't think Klopp wants to consider Lukaku because Lukaku seems not suitable with Liverpool game style. Liverpool is looking for a typical player that has a similar characteristic as Mane and Lukaku is clearly not the right option. Nunez is a good option to replace Mane's role in Liverpool squad although his transfer fees are quite expensive. And Nunez is still a young player who can play a long time.
Lukaku is a good player but the EPL is not a friendly enough league for this player, how many clubs has he been to and only at Everton did he play well but for big teams like Chelsea and Manchester United he can't do much there.
His vision of the game doesn't really match Liverpool, why should it be forced, even though in this case Liverpool still have many options for attackers but I don't think Klopp will make a choice for him, especially for Nunez, soon the contract talks will be completed.
The premier league suits him well by the way, the issues he had at Manchester United was clearly he's first touch on the ball and he's positioning, he left for Inter Milan and got that all fixed up,after the one glory he had over Inter Milan, he thought it'll be a great comeback to the premier league to represent he's boyhood club Chelsea.
But, they ( Chelsea ) at th moment are currently not playing to he's strength another big issue is that he is a left footed player and not really flexible and do stuff's swiftly. Chelsea are also not creating enough chances for h, he is not the kind of player that works or gets goals himself, the midfielder's and wingers have to do that to lay the Ball and Boom! He scores.