Probably due to treesitter modules for many languages compiled in. AFAK Treesitter's codegen is unfortunately a share nothing between different languages. So a dozen language parsers can easily cross upward of 200 MB.
Unless by "compiled in", some in-lining of the C code into Rust codebase is meant.
[1] https://github.com/emacs-tree-sitter/tree-sitter-langs/relea...