Why does this resistor network simulate differently from the physical package?
Wrong datasheet

Mouser links to the wrong datasheet.  The part number you have looks like ?????-R2R-??? but the datasheet you link covers parts with 101, 102 and 104 as that second group.  If you look at this datasheet instead:

https://www.bourns.com/pdfs/r2r.pdf

You will see that you have a SIP package R2R ladder with 100k resistors. If you look at the bottom left schematic in the group of four, you'll see that it does indeed have a resistance of 200K between pin 1 and pin 2.