Talk about exploitative. Hell, that's incredibly biased. Can you imagine a young parent being able to do that?
Most cheapo shops which won't pay FAANG salaries but still want near-FAANG-quality-engineers end up using this as a bait.
Other ways are "your work has great purpose!" "You will advance humanity!" "You will bring great experiences to users" ... yeah yeah yeah, just an alias for "we are a glorified bodyshop. BigCos hire us for some piecemeal job. We get it done and get paid relatively well." But this isn't too appealing, is it!
At least they are open about it. It is probably a fair indication of the companies values if they are oblivious to how unreasonable a 3 day take home assignment is.
It would most probably have a twisted answer as "you can post that solution of yours in your git repo and showcase it as a part of your portfolio"
Many shops out here are so adept at this stuff, it's no more funny!