why would Intel disable some of these features on their more premium
The reason the K Series (it's formal name) family or products does not have these features, is because those features you listed are being marketed to businesses, and overclocking the primary feature of the K Series is being marketed to enthusiast.
Intel positions TXT, in particular, as a purely business-focused
part—it's an integral component of the company's vPro platform—so no
doubt feels that it's irrelevant to the enthusiast (that is,
gamer)-oriented K series. This is true, in a sense—the only systems
likely to make use of TXT and TPM are business systems—but that's a
chicken and egg scenario. If TPM were in every Intel chipset and TXT
in every Intel processor, of course system and software vendors would
start using them.
While the quote was written several years ago, it still holds true, TXT and vPro are both marketed the business sector.
What processor should I buy? Intel’s crazy pricing makes my head hurt
It's called product differentiation and a company like Intel will not offer a feature on one version of a product in order to make it separate from another product in the same product family.
In economics and marketing, product differentiation (or simply
differentiation) is the process of distinguishing a product or service
from others, to make it more attractive to a particular target market.
This involves differentiating it from competitors' products as well as
a firm's own products. The concept was proposed by Edward Chamberlin
in his 1933 Theory of Monopolistic Competition.
Are there K-Variant chips that do not have these features disabled?
The features are indeed not enabled, they are not disabled, they simply were removed.
Is it possible to enable these features on a K-Variant chip?
The feature cannot be enabled because it doesn't even exist.