Aside from having a normal and an XL model, it seems that Google isn’t really a fan of having two of something.
It doesn’t have two main cameras nor does use the full extent of dual SIM capabilities.
One of those might be changing in the upcoming Pixel 4 phone later this year and, no, it won’t be the cameras.
A Googler commenting on a source code change for Android Q let it slip that the 2019 Pixel will have “dual SIM functionality”, which hopefully means the true dual SIM capabilities users expect these days.
In truth, the Pixel phones since the 2017 Pixel 2 actually have dual SIM support.
Like Apple’s newest iPhone, those Pixel phones have a tray for one SIM card while the second is provided by an eSIM.