LiPo batteries were quiet expensive when it was initially released. NiMH was really the only option in town.
And with a lower energy density battery that's also heavier, adding a cooling system would have also added a bunch of weight to the already heavy car with a barely usable range of 100 miles.
Gen 2, however, had no excuses. They had every opportunity to add active cooling and they still decided to go with just air cooling.
Edit: Checking Wikipedia to verify my information, I found out that Nissan actually sold a lithium-battery EV in 1997 to comply with the same 90s CARB zero-emissions vehicle mandate that gave us the GM EV-1: https://en.wikipedia.org/wiki/Nissan_R%27nessa#Nissan_Altra
Even just looking at online media reports[2][3] clearly sourced from some exact same press event, it is obvious that US English equivalents are much lighter in content than Japanese versions. They're putting the information out, no one's reading it. It's just been the types of information that didn't drive clicks. Language barrier would have effects on it too, that Toyota is a Japanese company and US is an export market, but it's fundamentally the same phenomenon as citizen facing government reports that never gets read and often imagined as being "hidden and withheld from public eyes", just a communication issue.
1: https://www.toyota.com/priuspluginhybrid/features/mpg_other_...
2: https://www.motortrend.com/news/toyota-aqua-prius-c-hybrid-b...
I was looking up this year's Corolla a while ago and likewise there was minimal info that I could see about the battery capacity, which I think I figured out was about 3kWh.
It's under Weights/Capacities but you have to expand the section yourself, no way to link directly to it.
/out
I use it in my driveway to make it look to thieves like someone is home (round me, houses with no car get broken into).
It seems like procuring the battery is not as expensive as the Tesla battery (I see someone who did it themselves for $6k on Youtube with the battery from a wrecked leaf). In comparison, the cost I see for my Model 3 is about ~$18k CAD.
Getting a car up and running for $8k might be worth it if it is otherwise dependable, but I've only heard unfortunate stories about the first gen Leaf.
The Lizard pack in the later Nissan Leafs has held up surprisingly well. I have a 2015 that still gets 75 miles of range. I'm sure they thought it wasn't necessary and they probably had the actuarial numbers to justify it.