I think bikes intended for touring on pavement run lower bottom bracket heights than off road where ground clearance may be a bigger issue. Of all my bikes, I think my expedition bike (Thorn Nomad MkII) has the highest bottom bracket at 11.75 inches (roughly 298mm) with 50mm tires. When I run 57mm tires, it is even higher.

Lowest bottom bracket on my bikes is on a 1961 vintage Italian racing bike (Ideor) at about 10.625 inches (or about 270mm). On this bike I run a 170mm crank instead of a 175 to get the pedals a little higher. When I was a kid I would hit the pedals on the ground when I pedaled while cornering. But I am a bit older now, I do not pedal in tight corners, so I could probably run a 175mm crank. Every time I ride that bike and stop at a stoplight, I am always surprised how high the ground is when I put one foot on the ground. And it is easier to get my leg over the saddle when I get on it.

In other words, I think 270mm is ok for touring on pavement with a 175mm crank but I would not go lower, and forego the pedaling in corners. Since rails to trails routes are as good as pavement when it comes to clearance, that should be fine too.

A photo of the Italian bike with low bottom bracket, note that I have something propped under the pedal to hold the bike up for the photo. And yes, the bike has a few modern parts on it, it is not fully original.