Kakoune fully embraces the unix philosophy, even going so far as relying on OS (or terminal-multiplexer, e.g. kitty or tmux) for window management (via client/sever, so each kakoune instance can still share state like open buffers).
A comparison going into the differences (and embracing of the unix philosophy by kakoune) by someone who uses both kakoune and helix: https://phaazon.net/blog/more-hindsight-vim-helix-kakoune
Sensible defaults and easy setup are a big deal. No one wants to fiddle with setting up their lsp and tree-sitter. There's probably more to their differences in popularity than just this, though.