I know in Domestic Class J they reserve quite a few seats for OW Emerald members. They've changed the system now so it actually recognizes my status during the booking process, but I used to have to book first, then go back in and select after I bought it to get the restricted seats. I know their international business class has similarly restricted seats, but I can't speak for economy. This is a trend though of a lot of airlines these days on lower fares, in the US and some in Europe, basic economy tickets are common which are also very heavily restricted unless you're a status member. Even airlines that you might think of as premium are better monetizing their seat selection, whether that's for direct buy ups for better seats in economy or restricting certain low fare classes to only really undesirable seats (encouraging the passenger to buy a higher fare).