what if someone want 104 or 105? that will take a lot of time packing specific numbers of covers in one single bag,
200=104/105+87+some left over( if you lost or break a couple of them)
200= 3*GH60 +some left over also!
Most of the time when you see springs or switches for sale it's 100, the reason is that most mech users have a TKL or even a 60%, the full size boards are simply not as popular.
Your argument is that somebody with a full size has not enough, and if he has a TKL as well 200 would be pretty perfect. Well why should that person not be able to buy 2x100? By forcing 200 per order you only get that people are splitting up orders, and that will end in less ordered covers:
With 200, one order is enough for 3 60% boards, so three people with each a 60% can split up that order. Then you sold 200 covers.
With 100 pieces per bag you will have 3 people who each buy a bag, they won't split orders because there is not enough for two boards, and the buyers probably won't mind having a few in spare. Then you sold 300 covers.