Sims 4 repeatedly installs to both drives

Have a peek under the Origin > Application Settings > Installs and Saves
Make sure those are set to the D drive. 

You'll also have a The Sims 4 folder in your Documents, this is normal and you can't really move that one with a setting. 
This is a rather old link that worked for someone to move the entire Documents folder, but I'm not sure it still works:
http://modthesims.info/wiki.php?title=Game_Help:Change_Location_of_Downloads_Folder

@Phantomlover1717 @kreatora

Unfortunately, this isn't related to the installer/saves folder. I currently have four directories for Sims 4:

C:\ProgramData\Origin\DownloadCache

C:\Users\orbit\Documents\Electronic Arts

D:\Origin Games\The Sims 4

The above is just fine and as expected, although I'll probably change the DownloadCache to my D drive.

The issue I'm having is with this directory:

C:\Program Files (x86)\Origin Games\The Sims 4

No other Origin game has a directory in the Origin Games folder on my C drive. As I install additional expansions/packs, the folder size increases. It appears as though it's installing the base game to my D drive but installing all expansions to my C drive — or at least that's my assumption after seeing the Soundtrack folder which is part of the deluxe edition I gained access to from Origin Premiere.

C Drive:

 D Drive:

@Phantomlover1717

The explanation on how to move the Documents folder are still correct for Windows 8 but needs a little change for Windows 10. It is probably best to point to this article: https://www.windowscentral.com/how-move-default-user-folders-new-drive-windows-10

D:\Origin Games\The Sims 4 and C:\Program Files (x86)\Origin Games\The Sims 4 sound the same. 
Did you install it before changing the drive? I've ran my Sims from an external drive for a few years, just moved that folder over and got Origin to find it again. You could try removing the folder from that location and testing if the game will still run if you do so.  

@jpkarlsen thanks bookmarked!

@OrbitStorm

By changing the installation address of the game to D drive, you have not written it correctly. Should be D / Program Files (x86). This would create a second Program Files folder (x86) on D drive and you would avoid trouble. The game will always be installed primarily in the  Program Filles folder because it has such a target address.

For now, uninstall the entire game from the computer. Clear computer with cCleaner and install gre correctly D / Program Fille (x86) /Origin Games

Exactly as I have it - I also installed the game on D drive

 You can remove the current game folder from Documents to the desktop and then paste your "saves" and Tray folders into the new game folder created after this reinstallation in Documents. You will not lose anything in this way.

@Phantomlover1717 No, never installed it on this PC before. Have Madden, BF5, and a few other Origin Vault games installed to my D drive without issue. It's just Sims 4 doing this.

@kreatora This was a fresh installation. When I said I changed the directory, I mean I changed the directory in the installer from the default directory for the C drive to a directory on my D drive.

Have you tested if the game still runs when you take the folder out like I suggested?