You are quite aware of the fact that WRP creates situations where the time of release from the pit stop can create environments for teams to make suboptimal flight decisions. TK and Rachel in AR12 were famous for that.
However, the main reason why teams would not get on the latest and quickest set of flights is lack of knowledge by either a travel agent, airline ticketing agent or racer. If you ask for the schedules for PRG LAS, you would get an array that most certainly does not include any of my flights and also not yours. That is no surprise since we developed them by leg by leg to get the best possible results. Airlines reservations systems do not always do that, particularly if 3 or 4 legs are required or if it is not a "normal" way of going from point a to point B. It would be easy for teams to take a less than optimal routing/schedule.
On the specifics of Madrid to Mexico City, the array of alernative flights offers me these:
IB6403 1250 1805
AM002/UX3221 1430 1945
MX1587 1510 2050
There is no mention of any IB6401, although it is obviously close to a real flight number for a different time.
When I check the Iberia Airlines timetable, there is no mention of IB6401. The only Iberia plane which landed in Mexico City yesterday, a Friday, was IB6403. However, it is possible that IB6401 was terminated between 8/7/09 and 10/2/09. In fact, Flightstats does indicate that flight for departure from MAD 0120 and arrival in Mexico City 0616.
So, you have an obscure though real flight and an obscure route. How could people miss it? Easily. I did and I did an exhaustive serach of the US and Canadian largest airports but never gave any thought to whether major Mexican airports should be included. Why would a travel agent think of it?
I am not about to toss my above routings and schedules just because they are not the absolute best. We will see what actually happens. The latest departure I was able to develop was 1625. If it turns out that the pit stop release was after 1530 and before 1900 , then the only possible alternative will be your routing.