[abcdef123xyz123]

It isn't really implicit, it is just a shorthand, new is short for new-session and attach for attach-session. The alias for list-sessions is "ls" not "list".

I don't know why you would say -s shouldn't be required. Are you suggesting that "tmux new -sname command" should be something like "tmux new -ccommand name" instead?

The intent of -t is that it works much the same for all commands.

Of course you need to read the manual for anything more than the very basics, but tmux is hardly unique in that. Vim is hardly intuitive in any way.