Page compression not working?
If you're using big fields like VARCHAR(MAX), you'll discover that off-page data isn't compressed with page compression. (Hey, go figure.)

To see how much data of your table is being stored off-page, use the free open source script sp_BlitzIndex (disclaimer: I'm a coauthor on that). You can run it at the table level like this:

EXEC sp_BlitzIndex @DatabaseName = 'mydb', @SchemaName = 'dbo', @TableName = 'whywontthiscompress'


Then, in the top result set where it lists the indexes, look at the amount of LOB data stored on the table. If it's a lot, that's probably why compression isn't working. (And you can post a screenshot of the top result set in your question if you'd like more help/clarifications on this.)