Most people, especially younger people, want skills they can use right away for self-defense and fighting. So, most will not have the interest or patience to work on internal body method. That's a reality. Internal training takes huge amounts of solo work -- the antithesis to "learning to fight." The men who became legendary as internal martial artists mostly were training in hard fighting arts before they discovered "internal." If they learned internal methods earilier in life, it seems that it's because they began as children entrusted by their fathers to the training and influence of an accomplished internal martial artist. (example: Sokaku Takeda's student Sagawa claims to have learned "aiki-age" (pengjin) at 17.) Or, their fathers (and maybe mothers) -were- that accomplished teacher and they thus got indoctrinated in the skills as soon as they showed the physical and mental ability to train.
The rest of us lesser folk just wanted to learn to kick ass.
To play devil's advocate for a paragraph, I have to point out that coming into internal training after having trained "external" (whether MA or physical training such as power lifting) for a long time, can be detrimental to inculcating the "wiring" and habits of internal methods. It can take years, for example, to undo the wiring for firing shoulder and upper back muscles, torquing/twisting the hips to punch and strike, and other mechanically different methodology.
That said, people coming into internal training from no martial background don't seem to learn internal method any faster or sooner than fighting-trained people do, except allowing for individual talent. The former may not have the "external arts" wiring of the latter to undo, but they do come with their own individual body habits that need to be re-trained to accept the new way of moving and being. Some teachers say they'd rather teach students with no prior MA training, and I can see that "tabula rasa" as appearing to be easier than erasing some other teacher's work and inputting one's own. But question whether that's really always true.