Notice that the TeX you have installed locally is many conversion steps removed from the WEB source.

Pascal code is extracted from the WEB. Then the Pascal is translated into C. Afterwards, years of development have accumulated on that C source to handle utf-8, modern fonts, PDF output, etc.

Most work nowadays happens on top of LuaTeX that replaces and extends pdfTeX.

There are shockingly few people maintaining that core of the TeX environment.

The source control is mirrored here: https://github.com/TeX-Live/luatex/tree/experimental