Because if everyone voted, it would be prohibitively expensive to gerrymander down to small areas such as individual city-blocks. You may have a generally Republican area but a small area/block within would be Democrat because of (say) a respected church leader, for example.
Also, older people vote at much higher percentages than the young and are usually much more settled. If everyone voted, then gerrymandering would have to deal with a population much more in-flux, and the partisan areas would be much harder to identify and maintain.
If you had 1,000 people voting, it would be very easy to gerrymander; 330M people not so much.
"Because if everyone voted, it would be prohibitively expensive to gerrymander down to small areas such as individual city-blocks. "
Citation needed.
This is honestly a pretty trivial ILP problem.
Certainly you realize they already know each individual voter's political affiliation if they've declared one or votedin primaries?
The data set also includes their address,etc.
I've seen the data they used.
Heck, we were the only ones who asked the data providers to not include people's names or other PII (we just wanted to map street segments to political districts), and they pretty much laughed and said nobody had asked for that before.
Also, older people vote at much higher percentages than the young and are usually much more settled. If everyone voted, then gerrymandering would have to deal with a population much more in-flux, and the partisan areas would be much harder to identify and maintain.
If you had 1,000 people voting, it would be very easy to gerrymander; 330M people not so much.