They do this semi-regularly, the last one was some sort of hidden object puzzle which I just couldn’t be arsed to do, but this one was straightforward about it: this game, these conditions, 60% off. It was a new lowest price for Thronebreaker so I happily took advantage of that.
If I were cynical, I’d say that by making the deal exclusive they want to make it appear more enticing so that people will be more likely to buy it even if they wouldn’t have paid for a non-exclusive deal. If I were idealistic, I’d say they’re simply throwing loyal customers a bone with a discount on a game they’re probably interested in, given their ownership of a similar one. (The other deal was for X4: Foundations if you owned Freespace 2) Could be both?