Backup up the log does not cause it shrink. Backing up the log marks parts of it to be available for re-use. You must run a DBCC SHRINKFILE to reclaim the space on disk.

If you are looking at the initial size in the SSMS database properties I believe that actually shows current size. They call it initial size for when you are creating a file.

Right sizing the transaction log is important as you can get a fairly significant performance hit if it needs to grow during business hours and having a log file that is too large can also be a hit when doing disaster recovery.

If you aren't doing regular log backups, which will help maintain the log at a reasonable size, and you don't need the ability to restore to a point in time, you should change the recovery model to SIMPLE.