Because "lithium" means a whole category of things. See this mega-thread that was started in 2011 when people will still feeling things out:
* https://www.cruisersforum.com/forums/f166/lifepo4-batteries-...
The chemistry of LiFePO4 was settled on (versus something that used cobalt, à la Boeing's 787), and the risk of fires has been reduced considerably. You're more likely to have a boat fire from bad DIY electrical cabling and a lack of fusing.
For more than you ever wanted to know about marine electrical/electronics see Jeff Cote's channel:
* https://www.youtube.com/user/pacificyachtsystems/videos