Perhaps this is, as Tractinsky points out, because aesthetics and other design principles are intertwined and the specifics of design as tested are not sufficiently delineated.
As is also mentioned in this chapter, terms such as “aesthetics” or “beauty” are ill defined, originating in diverse disciplines in which different meanings of the terms prevail.
The psychological perspective further exacerbates the development of theory since it is difficult to determine precisely why a user responds to design elements.
Along these lines, what exactly is pleasure? How is it different from enjoyment or satisfaction?
Although some studies are aiming to disentangle these various constructs as reactions to design, in the realm of affect and emotion there is much work yet to be done.
Developing or adopting theoretical frameworks that underpin such emotive or affective responses is essential to the development of design theory that can be tested over time in diverse contexts.