I think you are spot on with “Frequency matters”
I think one thing here is you are also competing with people doing the move themselves (potentially w/ friends and family). That is a big limiting factor on price for a rarely occurring event (going back to “frequency matters”). Moreover, for people who value the convenience of not doing things themselves over price, those people will tend to value the convenience a lot, so that moves you into the high end tier again.
This reminds me a little of my work. I work for a software firm who sells software testing tools and I know for some companies who are only going to do the extra level of testing once or twice, our software makes no sense since they can cobble together an ad hoc solution that will work good enough, even if it is painful to set up (part of this is that no matter what doing that extra testing is always going to be somewhat painful, even with tools). However, for people who are doing extensive software testing repeatly (due to regulatory concerns, quality concerns, or the cost of fixing defective software in the field), our software tools fit a good niche.
There might be a market for Walnut in frequent movers, but frequent movers tend to optimize things so that it is easier to move things themselves so I’m not sure there is a market there.