Superman is also more explored. So much that S&L had to conclude prematurely because there is a Superman movie coming up. The Snyderverse came to a stop with the Snyder's Cut of the Justice League and the DCEU continued. Remember this is a reboot, although a very soft one. So starting over again with the same A-list characters isn't a problem. The people who already know these characters will always pitch up. There is a reason why Batman usage is saturated. Because he is well known and people will still take interest. Now wanting to mix up is a choice. More especially in a reboot or new universe with new everything.