I"m thinking you had a highly fragmented table that has never had an index rebuild. Does this table have a Primary Key and/or Clustered Index (usually the same one), if so it has an index. If not, then why not. When you copied the data it was copied with all the data compacted and only taking the space necessary to house it. The first table appears to have been subjected to extensive page splitting..
You need to periodically reindex your tables and update stats. The optimization jobs will help with parts of that. 8GB is big but not that big for a table..