Because the 885 literally cannot function as a scanner without GPS. There are no means to selectively program it or to manually select things you want to scan. It operates 100% based off of the GPS signal to determine location, which it uses to select the systems to scan. It's an extremely dumbed down implementation of Uniden's location scanning; imagine a 536 with no front panel that simply scanned the full database using nothing but the GPS coordinates to automatically turn the systems on and off as you drive along.
That's what the 885 is, and that is why it must come with the GPS puck, otherwise it's useless. The SDS200, and the rest of the Uniden full-featured scanners, are obviously able to function perfectly fine without GPS input. Don't think for a minute that the cost of the GPS puck isn't factored into the price of the 885, because it is. Not everyone should have to pay an additional $25-$50 for the SDS200 just for the convenience of the minority of purchasers getting the GPS puck.