Some of us don't want a DIY kit, and are not hard core enough to spend motorcycle money on an e-bike. My wife and I trust Costco for quality products, places like Wal-mart not so much.
Our GenZes came ready to ride, have a decent warranty and apparently excellent customer service. I got an emailed reply to a question in less than 15 minutes. As for issues like battery quality, forum member KenM. posted a long term review that included 5000 miles on the original battery.
BTW I have assembled a couple of clip-on gas engines to Wal-mart cruisers for a friend, and KenM's experiences with his match mine. They are junk, and pollute the air with noise and two-stroke oil smoke. The likelihood that they are no longer functional is a bit comforting, though.