Consider the Player version as a limited demo/trial version. You own Kontakt 5 and can fully test K6 to check to see if it is worth purchasing as can anyone who has never used Kontakt before.
If you upgrade from K5, NI have generated some return.
If they sell K6 to a new customer, they have achieved what they set out to do which is attract a new source of income.
All the limitations are there for commercial reasons.
There are libraries that work without limitation in the Player version, but they require a license fee to be paid by the library creator to NI. That is why most of the libraries that work in the Player without limitation are commercial libraries.
With Claustrophobic Piano you could use the free Decent Sampler by Dave Hilowitz as an alternative;