SQL Server 2012 Agent Job not providing full failure message for SSIS Packages
SSIS handles errors in two ways.

One is raising an error.
The other is failing a task/container/package.

The two are actually quite separate, and you can easily see one without the other.

To bubble an error up to the client (in this case, SQL Agent and its log) you would have to avoid catching the error somewhere. I suspect you might have an error handler there in some, or you have some of those convenient red arrows in there...

Of course, I see many times when people have errors that aren't causing anything to actually fail, so the package just keeps running. But that's another story...