17gb backup to cloud uses 100gb cloud storage

I am trying to use the sync to cloud option, one of the main reasons I bought the premium product with 250gb of storage.

However when I sync folders to the cloud they always take way more storage in the cloud than they do on disk. for instance I set myPictures of 59.gb to sync to the cloud and it ran out of storage before was anywhere near complete.

I tried another folder of 17gb abd it has taken 100gb in the cloud.

can anyone advise please ?