I think what happens is that a module goes bad, not the whole pack. Also, people don't need 400+ volts and/or $10k of batteries for their house, they need something for the charging system which is typically 12/24/48v
A good BMS can mitigate the loss from individual cells going bad.
$10K is on the low side for most people forking out money for powerwall-size systems. The reason some people use old EV batteries is because they're cheaper than buying a bank of LFPs, even when you buy cells in bulk and assemble the batteries yourself. Before the pandemic caused the world to go crazy, people were buying used Chevy Bolts because it was cheaper to buy the car, park it forever, and tap into the battery system than it was to buy batteries by themselves (and the Bolt has a really simple HV battery setup that's easy for a competent DIYer to work with).
I've also seen folks on the RV forum using modules (though usually just one, not an entire pack).