To make that possible you could release a single smaller core rulebook with just the core rules and then have the Edge, Rebellion and Destiny stuff as separate sourcebooks. The problem there is development time VS return. To do that they'd basically have to shove everything out in pretty much one big bang. Which is expensive for our wallets and for theirs.
No, you'd just have to release the core rule book and the Edge of Empire book. You could still release the AoR and F+D books later and it would make no difference to those of us currently playing EoE. It's not exactly unprecedented - Players Guide and Dungeon Master's Handbook spring readily to mind. Imagine if for every D&D setting you had to buy the Players Handbook over again? Happy you would not be.
Or an alternate approach would be to release EotE as is and do AoR and F+D as supplements. More space for material you would then have. You'd lose on people having to buy the EotE stuff regardless, but who doesn't want Smugglers and Marauders in their game?
Regardless, the first case provides equivalent to what we have without the duplication and without any reason you'd have to release everything at once as you claimed.