Typology - A hypothesis on why so many INFPs type as INFJs.
If we take a look at the functional stack of the INFP vs the INFJ, we see that one is an intuitive dominant and the other is a feeling dominant:
INFP: Fi - Ne - Si - Te
INFJ: Ni - Fe - Ti - Se
This also means that there is an inferiority complex surrounding the Thinking function for the INFP, and there is an inferiority complex surrounding the Sensory Function for the INFJ. Let's look at the particularities of these inferior functions.
Te - Objective decision making and gathering of factual evidence and empirical data, organization of the environment in a logically correct manner.
Se - Objective observation of present data, the reliance on concrete data to support the decision-making function.
If we take a look at the INFP's dominant function, Fi, we see that it is centralized on individualism, emotionalism, and uniqueness, meaning that the INFP's focus is to essentially be a unique individual that stands out from the crowd. This, of course, draws them to the esoteric and mysterious so that they can self-actualize and be unique, and what better way to ensure uniqueness than to be among the few? This of course can lead to the infamous INFP -> INFJ mistype, but how can we tell the two apart, especially if the mistypee is adamant in his or her mistyping? The inferior function.
INxJs' already established inferior function is Se, meaning that they are less likely to face the reality of a situation or the present circumstances, allowing them to cling to the dominant perspective of introverted intuition and focus a majority of their time on the past and future.
IxFPs' already established inferior function is Te, however, meaning that they are less likely to face objective facts and empirical data that is put in front of them, instead clinging to their Ji dominant perspective and focusing on their uniqueness and individualism (an exemption to objective data almost?).
When the inferior function is expressed negatively, it is avoided and ignored; therefore, we can conclude:
The average INFJ doesn't want to be forced to face the present and reality of a situation, and thus avoids it all costs, clinging to the dominant function (of idiosyncratic possibility convergence).
The average INFP doesn't want to be forced to face the facts and objective data concerning a situation, and thus avoids them at all costs, clinging to the dominant function (of individualism and emotionalism).
The INFJ avoids reality, and the INFP avoids facts.
I'm sure you can guess what this leads to without further discourse.