Originally, the project had a goal of zero dependencies. [1] I assume that was considered infeasible with the migration to Rust, but part of the philosophy remained.
[1]: http://web.archive.org/web/20201101030019/https://rome.tools...
[1]: http://web.archive.org/web/20201101030019/https://rome.tools...
It’s an extreme approach that intended to get extreme results. One could definitely argue that you can get just good results with a good approach (like using a bundler to produce a single output, writing perf-sensitive code, continually testing for perf regression), that’s just not the path they chose from the start.