Think of it this way. A collection of OSS'
Meh. bad comparison. but the point stands, that a Collection without anything special, is only really going to attract fans who DONT have the games.
AC had navi mode and the two arcade games, as well as some interesting bonuses, XC had the PSX X3, (which really is a matter of personal opinion on whether you like it or hate it) had weak extras, but we didnt have MMOCW, so its excusable, since not all of it was online actually. It also had Battle and chase.
For example, I only played X4- on, so I bought it since it had 1-3.
But Zero collection so far, from what weve seen, has all 3 games, unaltered, and an image gallery of common ZCW art that we have definitely already seen. And it may OR may not- have the Z3 modifier.
I have Z1,3, and 4, so theres no reason to buy it just for one game, thats on a system that isnt TOO past gen yet.
Im sure others are in similar positions, only missing maybe 1 game, or might already have them all.
And if their plan is to raise some dough, and interest for a ZX3, (as seems to be the case) then they would want everyone to buy it, regardless of whether they have the games or not.