This happens because the drug is very highly priced (almost $450 per month) and insurances have a herarchy of "best results, less priced" drugs that they believe a prescribing physician should consider before aiming at such a high priced drug.
I can tell you with certainty that modafinil would show up on lab screen done for employment.
Second, modafinil is not that good of a drug anyways (or nootropic). It basicly wakes you up a little, then it gets you crashed when it wears off.
I have also found that using brain entrainment along with nootropics is a REALLY powerful way to crank up your cognitive power for a short period of time.