Maybe it's just that many people find 16GB is enough for their use cases :) (I actually cannot think of any use cases for an ultra-portable when you would actually need more than that)
This applies to normies too. I mean, it's nice to have (web/g/hot)mail, slack, skype, messenger, element, discord open in the background while surfing the web and I doubt that 16GB will be enough for long.
What if I want to run photoshop and illustrator at the same time? Heaven forbid, they rewrite those power tools to run on electron.
As someone who splits his work between a 64GB workstation and a 16GB ultraportable, there are a ton of use cases where 16GB is a perfectly acceptable amount of memory. That said, 32GB of soldered memory is feasible in a ultra-portable these days so it would be nice for Lenovo to get with the times.