Why my openwrt support wget instead of curl?

To install packages supporting https:

opkg update
opkg install -d  usb  ca-certificates openssl-util ca-bundle  
opkg install -d usb   libustream-mbedtls

wget works fine for https.

wget $url
Downloading 'https://saimei.ftp.acc.umu.se/debian-cd/current/amd64/iso-dvd/debian-10.9.0-amd64-DVD-1.iso'
Connecting to 2001:6b0:19::138:443
Writing to 'debian-10.9.0-amd64-DVD-1.iso'

Check curl.

curl -o debian.iso  $url
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
curl: (77) Error reading ca cert file /etc/ssl/certs/ca-certificates.crt - mbedTLS: (-0x3E00) PK - Read/write of file failed

Why wget works fine instead of curl?How to support curl then?

is the file actually there ?