There's a difference between things liked by core fandom and those that might attract a wider audience. Publishing tries to balance the two, usually tending towards the latter, although I'd argue Rebellion if anything cares at least as much about the core fans, given the trades we've got over the years. So Ennis is something of a no-brainer, given his reach outside of the UK, and also when you bear in mind that initial run of trades was done in collaboration with DC Comics.
And, yeah, that early selection was a bit scattergun, and you could feel that Rebellion felt a bit hemmed in, given that it also released its own line of hardbacks with more oddball characters lurking within. (I recall when that DC deal ended, and wondered what would happen next. Little did we all know at the time it was probably the best thing for everyone. Just looking at the trade line Rebellion's done in those years since is really quite the eye-opener.)