Player development, PLUS guys staying for 4-5 years can overcome a lack of top end stars. That said, you also have to hit on your evals at a high rate, to make up for the fact that you don't have ready made stars coming in. However, TCU is an OUTLIER. I know our fans have difficulty understanding what an OUTLIER is , so I'm going to provide a definition.
out·li·er
/ˈoutˌlī(ə)r/
noun
a person or thing situated away or detached from the main body or system.
"less accessible islands and outliers"
a person or thing differing from all other members of a particular group or set.
"an outlier in Faulkner's body of work"
You look at the typical playoff team, they are rarely as mediocre in overall recruiting as TCU, in fact, it's rare that a program is consistently outside the Top 15 in the rankings makes a CFP appearance. Just like in the NFL, you are much more likely to find your franchise QB in the first round, compared to the 6th, but you always have someone screaming "Joe Montana and Tom Brady weren't drafted early", forgetting that the bulk of good QBs drafted in the last 40 years were usually taken in the top 2 rounds. Outliers don't disprove a rule, they only prove that in any dataset, that someone will be outside the standard deviation.