A few "two cents"/opinions from me, surely not the complete picture.
External crates are easy to include and often come also from rust core developers, this does not actually slows one down but allows for much more flexibility.
The big benefit over python is that rust does not dictates what you need to use.
And with the trait system you can often just plug in another, now maybe better fitting, solution for a specific crate.
Further, note that rust is normally shipped to the user compiled to a binary with all rust code statically linked in, while python isn't. Python is shipped often as code, and if the std library would not include that much that'd mean that one had to ship lots of module code along.
So, rust would not actually profit from having a big standard library the same way Python does.
Having a big standard library makes it also harder to deprecate and remove cruft (<https://lwn.net/Articles/790677/>), which can get a problem over the long time.
External crates are easy to include and often come also from rust core developers, this does not actually slows one down but allows for much more flexibility.
The big benefit over python is that rust does not dictates what you need to use.
And with the trait system you can often just plug in another, now maybe better fitting, solution for a specific crate.
Further, note that rust is normally shipped to the user compiled to a binary with all rust code statically linked in, while python isn't. Python is shipped often as code, and if the std library would not include that much that'd mean that one had to ship lots of module code along.
So, rust would not actually profit from having a big standard library the same way Python does.
Having a big standard library makes it also harder to deprecate and remove cruft (<https://lwn.net/Articles/790677/>), which can get a problem over the long time.