It was on purpose because TOML has not reached 1.0 yet and breaking people using a module in the stdlib for parsing TOML because TOML itself changed would be an absolute mess. Plus not a single packaging project said it was an issue to either depend on or vendor a TOML parser.

Once TOML hits 1.0 I plan to work on getting a TOML parser into Python's stdlib.

(disclaimer: I am one of the co-authors of PEP 518 that apparently handled things in way that was "a little absurd" .)

> The pytoml TOML parser is ~300 lines of pure Python code, so being outside the standard library didn't count heavily against it.

From the link. Makes sense I think.

The PEP has provisional status. Maybe before it lands it will be brought in.