People will go to matinees because the slot is appealing and possible, and, for the most part, people who have to take time off from work won't. Wednesday night is neither Opening Night, a traditional night out night, like Thursday (huge in the UK and Ireland and among macho young financial types in the US who can make it to work on Fridays after getting home at 3am or later) and Friday, nor a weekend. It's also not considered a "prestige" night, like Opening Night or Saturday night.
The only day-specific casting patterns I remember from NYCB were more soloists and corps members getting their chances on Saturday matinees -- I don't remember if this was true for Sunday matinees when they did two Sunday performances -- a majority of Principal Dancers' final performances were scheduled on Sunday nights, and there was lots of star power at the Spring Galas, usually on Thursdays, if I remember right and at the season finale Sunday night special performances. (Dancers' Emergency Fund benefit at the end of Winter Season; I don't remember what the Spring season closer was.).
Does ABT have a pattern of giving specific nights to the casts with the biggest names? Do Wednesday nights sell very well if the big guns appear?
Helene, I hate to sound ignorant, but I have absolutely no idea what the term "cast-agnostic" means. Could you explain it please if you get a moment?
"Cast-agnostic" means pretty much the same number of tickets will be sold no matter who dances, because people want to go on a particular day or time (or they want to see a ballet no matter what) or they can't make/dislike a slot. Subscriptions, for example, generally are cast-agnostic, unless they're to "All Opening Nights" or predictable based on experience about how a company casts. Another example is weekend matinees of "The Nutcracker," to which families will buy tickets way in advance of knowing the casts, and, if they're trying to make their five-year-old happy generally, won't care who's dancing, unless the Prince is their next-door neighbor. For people who travel to see ballet and can only come on weekends -- that's my situation with PNB now -- you can only hope that casting works out, which for me means almost always, as many permutations of casts as possible.
I passed up almost every matinee In NYC, except the year I was a full-time graduate student with night classes. The exception was a Paris Opera Ballet matinee for which I took a precious vacation day. It was my only chance to see Patrick Dupond, and it might have been the performance with Sylvie Guillem in second movement of "Palais de Cristal." [Edited to add: no, I checked: Guillem danced Tuesday night, 15 July 1986 and Platel, whom I loved, danced the Wednesday matinee, 16 July 1986.
The trouble comes when a person picks a day/time that yields them casting they don't like consistently. I've long had a first weekend (of two) Saturday matinee subscription to PNB. Until five or so years ago, Opening Night was a Thursday, and if there was ever a time that Patricia Barker, the PNB star at the time, was not going to dance, it was Saturday matinee. (She would have danced the Opening and would be prepping for the evening performance.). I would hear people around me open their programs and say, with disappointment, "No Patty," as if this wasn't predictable. Same with NYCB Saturday matinees: I got to see lots of the soloists -- Saland, Calegari, Fugate, Joseph Duell, for example -- make their debuts in roles and grow into Principals. For people who wanted to see Suzanne Farrell, who did a few ballets like "Davidsbundlertanze" in that slot -- it was a time when many elderly women were worried about taking the buses or subway at night -- it was an exercise in frustration.