Comment by volkl48
Now.
I will point out that in 2016 when they started this project, the cost of new batteries would have been multiple times higher than it is today, so it would have been a moderately more "sensible" thing to do than it currently seems.
Yes, of course, this cost consideration is only relevant today.
I can imagine that ~9 years ago there might have been very little reasonably priced LiFePO4 cells available and if someone could get their hands on used 18650 cells very cheaply, it might have been a reasonable choice at the time.