People do seem to often complain about the tmux defaults or say their particular configuration is "sane" and the defaults are not. But if you look at changes people make or at requests made over the years, they are all over the place and there is rarely a single common consensus on how the defaults could be better. Even if you look at something like "tmux-sensible", it is maybe a dozen lines of changes, of which some are now obsolete, some have downsides that prevent them being the default , and some are obviously personal preference.

I did have new panes and windows default to the current working directory for a while, and I in fact do this in my own config, but there are security concerns and it was felt it was better that people have to configure it explicitly if they want it.