It’s a marketing strategy.
Whenever I see a swgoh ad on another game, it’s an ad about something that’s already passed. So if they advertise the BB-8 event 3 days after it’s finished (Which they did do!), people interested in BB-8 start playing and work towards him. If you could get him right away, you would lose interest after achieving him. They make you stay longer this way. Kinda get what I’m saying?
I just saw an advertisement on Leap Day:
New Characters:
The Triumvirate!
If you had joined to get Sion, and they released a pack every two weeks for him, you would buy Sion and then get bored.