Probably because you've got loads of junk on there.
The largest wastes of space are channels such as Mario Kart channel, Wiifit channel, Wiiware and to some extent Virtual Console.
If your Wii is 4.0+ then drop the Wiiware/VC channels to SD to clear loads of space.
By the way I have over 70 games on HDD and every one has a save, I've also never needed to copy one to SD. I only have 1 VC channel, all others are on SD.
If your Wii is <4.0 then use Triiforce to load Wiiware/VC games off emulated NAND on your SD card.