That is how it works - and there are no user options with respect to that
How many photos are stored in My Photo Stream on my devices and computers?
iCloud pushes all your photos to the My Photo Stream album on your devices and computers, and manages them efficiently, so you don’t run out of storage space.
Your iOS devices keep a rolling collection of your last 1000 photos in the My Photo Stream album. From there, you can browse your recent photos or move the ones you like to your Camera Roll or another album to keep them on your device forever.
Because your Mac and PC have more storage than your iOS devices, you can choose to have all of your My Photo Stream photos automatically downloaded. In iPhoto or Aperture preferences on your Mac, select Photos (or Photo Stream) > My Photo Stream > Automatic Import. All of your photo stream photos will be imported into your Events, Projects, Photos, Faces, and Places folders in iPhoto or Aperture. On your PC with My Photo Stream enabled in the Control Panel, all of your photos will be imported into C:\\Users\<user name>\Pictures\iCloud Photos\My Photo Stream. For iCloud Control Panel 2.0 to 2.1.2 users, the path isC:\\Users\<user name>\Pictures\Photo Stream\My Photo Stream .
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