Was this coupon a Bitcointalk exclusive coupon? Sadly, I read your post today, clicked on claim now button and I was late to use this coupon.
This coupon is available for all users who are also sent via email but to claim it at least your account level is silver and yeah they sent this coupon 2 times $5 and $8 if you see the BITCOIN price reaching $100k, maybe they will send another coupon, just wait in your email.
Admin not focus on this forum so he only posts a few while other users are not active because there are no campaigns or event, just try to contact the admin who knows he needs you to manage this thread. I don't know how they reach new users because they are not active in promos and ads while new competitors come almost every month, I rarely play here because I have other favorite sites and the marketing team should realize this.
Bitsler had a long running signature campaign as well as promotions in the past, I was one of their signature campaign participants for more than 2 years IIRC.
Every start must have an end, maybe they think that what they spend here is more than enough and moving to other places to advertise.
If I have to guess, Bitsler feel that what they have now is more than enough, that's why they do not need to something to boost the exposure about their existence.
No one knows if they will come back to be actively promoting the site again in this forum, but it is absolutely possible because if I remember it correctly they relaunched the signature campaign few years ago.