Why libraries appear in DEMO MODE?

Because you are using Kontakt FREE Player and not Kontakt Full Retail Version.
ALL my libraries are compatible ONLY with Kontakt and not Kontakt FREE Player.

What’s the differences between Kontakt Full retail version and Kontakt Player?

Kontakt player IS intended solely for libraries encoded by Native Instruments.
This means their own libraries and 3rd party libraries that have paid a license fee to have their library produced in kontakt player format. 
However, the fact is that Kontakt Player and Kontakt are the same software - only the license key is different. The result of this confusing situation is that in Kontakt Player you can open a normal Kontakt format library ( like the free content that is available) but it will run normally for 15 mins or less before the demo period times out. After that, you have to re-start and reload the library.
The problem is that there is no way to authorise a non-kontakt player library - it will always time out. 
So, to summarise -you can open it, and run in demo mode, but you can't get rid of demo mode. 
So in order to use my libraries you need Kontakt FULL retail version 3,4 or the new 5 or future versions.