I don't think it's just a passing trend - online broadcasts have already become a normal part of theater life, just like live premieres. Theaters expand their audience (people don't have to travel to the city, elderly people and people with disabilities can watch from home), they get money from subscriptions and advertising, plus it's an additional PR machine that brings new viewers into the building for in-person performances - people who watched online and wanted to experience the atmosphere live.
Financially it might be profitable or unprofitable depending on how well it's done and how much money they spent on it, but it really helps in the long run - theaters don't lose the audience that would otherwise go to streaming services.