Index rebuild, data compression generated Large TLog
Regardless of your recovery model whenever an operation (index rebuild or reorganize) modifies a data page that page modification is put into the log.  In your case changing the fill factor can add more data pages, and move data to new pages.  SQL Server has to make room for the new data and to do that it has to keep track of the page changes.  The more pages that are changed, the more entries will be put into the transaction log.

In your case I would ask, what storage are you using, and what is your fragmentation like?  If you're using flash storage, I'd tell you that rebuilding indexes becomes much less important than it does if you're using magnetic storage.