Good question. I suspect that everyone who assisted the last time I visited the SSPX Chapel–a on Saturday–assist on Sunday too. Just a hunch about those folks. Parenthetically, last time there was a potluck after Mass, followed by a fascinating talk by the visiting priest, then Complines (sung, in Latin, of course) so it was a late night.
I did just assist at a Diocesan 5 pm Mass (OF) Mass and (funny, right after leaving this conversation) it was introduced as “Vigil Mass for the 14th Sunday in Ordinary Time”. I’ll probably assist at another OF Mass tomorrow since it’ll be boiling hot in the valley and my leased car is way over my mileage budget. I’ll take my trusty '62 along, as I did for today’s OF Mass–for the before and after Mass prayers. I like to finish the OF Mass just like a TLM Low Mass, on my own, with the Prologue, the Aves, Salve Regina, etc
Forgot my earplugs today but maybe I’m getting better at tuning out the OF after Mass chatter. shrug.