It sounds as though you're looking at this from the perspective of someone who had knowledgeable coaches and "plenty of free time" in high school and college? Not all of us did.
In my case, my high school track coach trained us with quarter-mile reps every day. The result for me? PRs of 2:06.7 for the half-mile, 4:49.1 for the mile, and about 11:30 for the two mile.
In college, the training program was better, but not outstanding. The result for me? PRs of 9:50-something for two miles and 33:01 for 10,000 meters.
As for having "plenty of free time" in college, I was an undergraduate at M.I.T., working to complete two degrees in four years, and also taking ROTC courses (which did not count for credit toward either degree) to satisfy the requirements of my ROTC scholarship and commissioning program. Not much free time, even before adding in cross-country and track. I certainly took my running seriously, but it was in the context of a life that was filled with sleep deprivation and academic stress.
Why was I kept on the team when I couldn't even break 10:00 for two miles most of the time? Maybe it's because M.I.T., being an academic institution rather than an athletic factory, didn't cut people from an athletic team just because they were slow. Besides, by M.I.T. standards, I wasn't really that slow. I was, in fact, one of the faster runners on the team.
Many years ago, a writer for Runner's World (which was a pretty respectable publication back then) remarked that there are potential 4-minute milers and sub-2:20 marathoners on every high school track team, but most will never get close to those levels, because they won't get the right training to produce such results. One can certainly quibble with the particulars of that assertion, but the basic point seems right to me. If you had the right coaching and running environment to maximize your potential, good for you (at least, if competitive running accomplishments are important to you), but many of us didn't have that early on. In my case, I simply learned about training on my own, and applied that knowledge -- imperfectly, to be sure -- to develop my running abilities over the years. And I surprised myself, as well as others, with the results.
Talent in distance running is an odd thing. Often, the only way to find out if you have any is to spend years training. Then, if things finally come together, and you start producing good results, people have a ready explanation: You had talent.