If defenders play further back to prevent cherry picking, and forwards move up to cherry pick, it leaves you 8 guys running around the midfield accomplishing very little. A lot of the current tactics of the game center on controlling the midfield, but if defenders don't come forward more, controlling the midfield will mean less. So basically, yeah, removing offside might "open the field," but it will do so in a way that will make that open space less meaningful and won't suddenly make the game more appealing.