The particular mode of distribution of code as a traditional standard library has downsides:

- it's inevitably going to accumulate mistakes/obsolete/deprecated stuff over time, because there can be only one version of it, and it needs to be backwards compatible.

- it makes porting the language to new platforms harder, since there's more stuff promised to work as standard.

- to reduce risk of having the above problems, stdlib usually sticks to basic lowest-common-denominator APIs, lagging behind the state of the art, creating a dilemma between using standard impl vs better but 3rd party impls (and large programs end up with both)

- with a one-size-fits-all it's easy to add bloat from unnecessary features. Not all programs want to embed megabytes of Unicode metadata for a regex.

The goal of having common trustworthy code can be achieved in many other ways, such as having (de-facto) standard individual dependencies to choose from. Packages that aren't built-in can be versioned independently, and included only when necessary.