Hi Jeremy !
We ask for this API, because on the one you mentionned I see:
"The SNCF API contains theoretical train data for the following commercial modes: TGV, TER, Transilien, Intercités.
The SNCF API also contains realtime train data for the following commercial modes: TGV, TER, Intercités."
For realtime, on this particular API there isn’t (I guess) real time Transilien, which was the reason of this module, and the use of the other API.
(Perhaps I miss understood their indications and give wrong information to bobbob601 ?)