It's the people, for sure.(Maybe)

Now I'm perfectly sure. Kinda.
I decided to use my best headphones and measure the amount of reverberation in Lourdes. In an empty church, in 60 degree weather, I got 3.14 seconds of reverberation while playing the organ. Yeah I know, that's pretty stellar for such a small church. (But it's nothing compared to a place like the Washington National Cathedral, where they get 9 seconds (!) of reverberation.) Contrast that to Christmas eve at midnight, when there was no audible reverb.Everything was terribly flat, and it ruined Hayden's wonderful mass setting.

But maybe it's not the people.Because (without any special equipment) There seemed to be a little more than two and a half seconds of reverb at the last chord of Sunday's recessional hymn. Maybe it's the weather.I know for certain that the organ at the other church where I practice sounds amazing during the summer. The reeds are more powerful and the reverb (which you can kind of hear in my low-quality recording) is almost shocking. I've gotten over four seconds of reverb before, and that was with flutes and strings.
That church, however, was made for an organ.It's tall and has a high barrel-vaulted ceiling with zero soft surfaces to be found.
Nothing but hundreds of square feet of glorious floor-to-ceiling hard surfaces.
That only confuses things more though. Lourdes is also convered in hard surfaces (plaster covered stone walls, marble flooring, solid wood pews, tile,etc.) and the ceiling even consists of a high pointed arch, but things are usually not that great acoustic-wise, at least not as great as one might surmise based on the make and materials of the building. It causes me to wonder whether or not they had one of those horrible 'acoustic paint treatments' when the church was restored so many years ago.
I will make one note though: There is one acoustic sweet spot in the church. The right transept, the pew closest to the confessional, sitting in it closest to the aisle. Everything that comes from the choir loft somehow gets shaped with a sound that you don't hear sitting in the nave. I only discovered it five months ago, during a postlude after mass.