Why do people use bigger cassettes for lower gearing when they could instead use smaller chainrings? I want lower (sub 1:1) gearing on my next drivetrain but also a decent range, reasonable spacing between gears and still be reasonably light.

While looking at different combinations of components, I noticed that:


1x options were not nearly as light as I expected, mostly due to the huge cassettes needed for decent range.
On 2x, large cassettes were killing my weight compared to "standard" road setups (50/34 compact double with 11-28 cassette).
Shimano GRX setups gain weight in all the components, partially negating their gearing benefits.


At this point, for a lark, I threw in some randonneur type cranks and the old heavy bottoms brackets that go with them, and noticed the numbers coming up not that much worse than modern drivetrains.

Furthermore, I found that some rando cranksets can be made to come with super small chainrings. One manufacturer I looked at went down to 42/26(!), and pairing this with an Ultegra 11-28 met my criteria and was the lowest weight combination. I'd love to buy an Ultegra 42/26! Just imagine what that would weigh!

So, why don't more people use smaller chainrings? Or the flip side to this question: why don't drivetrain manufacturers offer them?

Is this just the standard reason that "the bike industry is driven by racers"? Or am I missing some obvious physical thing that makes smaller chainrings inferior? Should I just give up and become a retrogrouch?

This answer seems claims that smaller cogs have more friction, but it doesn't seem like it would be a lot more, considering we have "small" cogs on most of our cassettes.
Gear ratio range.

If you decrease the chainring sizes you decrease the highest ratios available. It's not possible to make the gap between the chainrings much bigger and get decent front shifting so the large ring has to shrink with the small one.   

It's easier for manufacturers to make a wide ratio cassette that retains an 11 tooth sprocket and shifts well.