It's one of those strange quirks of using QFF that JFK-CDG (via LHR on BA) is 35000pts but JFK-MIA-CDG (on AA) is only 36000pts. However the taxes, etc can be either $279 (all BA), $32 (AA/BA) or $5 (all AA via MIA). Some people would also pay good money to avoid a transfer in LHR. The direct flight MIA-CDG also gets you into Paris at a very sensible 9am.