I'm posting my question here in hopes of finding someone who actually understands bike geometry from both a theoretical & practical perspective.

My question has to do with a bike handling quality i'm going to call "stability" and my test for that quality is how easy it is to ride the bike no hands. And, specifically, my question is about road bikes with smaller wheels. In this case let's say 20" wheels. I have experience with only one bike with 20" wheels - which I find extremely "nervous" & "twitchy" - but my conversations with others who have experience with 20" wheeled bikes is that this quality seems to apply to most or all bikes with these smaller wheels. And these bikes all seem to have trail figures that are significantly smaller than most 700c bikes - often having trail figures half or less than a "full-sized" bike. I understand that trail is not 100% of what makes up the quality i'm calling stability but it does seem to be a pretty good proxy for that quality.

So my question: Is there a bike handling reason (as opposed to other specific use consideration reasons) that bikes with 20" wheels seem to have been set up deliberately with very little trail and very "nervous" handling qualities. IE: if a 20" wheeled bike were given, say, 58mm of trail would that introduce other handling problems that are worse than "twitchy" handling?