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.

Particularly if you can narrow down a couple brands where it tends to be a single cell or two that goes poopy while the rest are still good. Driving around picking up dead batteries that only have 1-2 good cells per pack is a thankless job.