The error “base64: unrecognized option: w” is output in alpine linux

The alpine images seem to have a version of base64 which doesn't provide the -w option:

docker container run -it --rm alpine:3.9 base64 --help
BusyBox v1.29.3 (2019-01-24 07:45:07 UTC) multi-call binary.

Usage: base64 [-d] [FILE]

Base64 encode or decode FILE to standard output
    -d  Decode data

but if you execute apk add --update coreutils it's there:

docker container run -it --rm alpine:3.9
/ # apk add --update coreutils
fetch http://dl-cdn.alpinelinux.org/alpine/v3.9/main/x86_64/APKINDEX.tar.gz
fetch http://dl-cdn.alpinelinux.org/alpine/v3.9/community/x86_64/APKINDEX.tar.gz
(1/3) Installing libattr (2.4.47-r7)
(2/3) Installing libacl (2.2.52-r5)
(3/3) Installing coreutils (8.30-r0)
Executing busybox-1.29.3-r10.trigger
OK: 7 MiB in 17 packages
/ # base64 --help
Usage: base64 [OPTION]... [FILE]
Base64 encode or decode FILE, or standard input, to standard output.

With no FILE, or when FILE is -, read standard input.

Mandatory arguments to long options are mandatory for short options too.
  -d, --decode          decode data
  -i, --ignore-garbage  when decoding, ignore non-alphabet characters
  -w, --wrap=COLS       wrap encoded lines after COLS character (default 76).
                          Use 0 to disable line wrapping

      --help     display this help and exit
      --version  output version information and exit

The data are encoded as described for the base64 alphabet in RFC 4648.
When decoding, the input may contain newlines in addition to the bytes of
the formal base64 alphabet.  Use --ignore-garbage to attempt to recover
from any other non-alphabet bytes in the encoded stream.

GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
Report base64 translation bugs to <https://translationproject.org/team/>
Full documentation at: <https://www.gnu.org/software/coreutils/base64>
or available locally via: info '(coreutils) base64 invocation'