As alacritty/vte says itself, "not itself sufficient for writing a terminal emulator" and as the comment in helix says:
A fully functioning xterm environment is [a lot of work](https://github.com/zellij-org/zellij/tree/main/zellij-server/src) and slightly inefficient as pointed out by the comment above, we need to re-parse all possible terminal escape sequences and reinterpret them (https://github.com/alacritty/vte can help but that's just the parsing bits).