[tossandturn]

I honestly wonder why. I developed a portable small-quantity project a few years ago and designed in a 20AH LiFePO4 battery pack; it seemed like the only sane choice. The cost was slightly higher and density was slightly lower, but the difference was less than 10%. Not having to be concerned with battery failure modes was a huge advantage. But those factors must be different at larger scales; the largest scale I can think of where density matters would be for a commercial electric 18-wheeler tractor; what chemistry do those use?

[Animats]

Price. Ordinary lithium-ion batteries have dropped in price due to volume production and competition. LiFePO4, not so much.