China BBSHD complete bikes vs DIY

I'm looking to spend about $1,500 on a bike and I want to get the most for my money. I could always buy a conversion kit BBSHD + battery but I just don't know what bike to put it on. The other alternative is to look on Alibaba for an already complete bike like this,

https://f2rq3.app.goo.gl/?link=https%3A%2F%2Fm.alibaba.com%2Fproduct%2F60586206521%2FQ7-48v-Chinese-Bafang-BBSHD-1000W.html&apn=com.alibaba.intl.android.apps.poseidon&ibi=com.alibaba.sourcing&isi=503451073&amv=69

https://f2rq3.app.goo.gl/?link=https%3A%2F%2Fm.alibaba.com%2Fproduct%2F60692945686%2FNew-brand-2017-bafang-BBSHD-mid.html&apn=com.alibaba.intl.android.apps.poseidon&ibi=com.alibaba.sourcing&isi=503451073&amv=69

Is there any reason why I shouldn't buy a ready made bike from China? How is the frame quality? I'm no expert on bikes but I can see a significant price difference cutting out the middle man.

Buy a good quality used bicycle and install your kit on that.
Look on Kijiji (Canada) or Craigslist (US/Canada) or Pinkbike.com
Look for brands like Specialized, Rocky Mountain, or even Trek.
Any bikes from department stores like Walmart are just shit.
A step up from "Just Shit" is the Bikes Direct website.

https://endless-sphere.com/forums/viewtopic.php?f=3&t=89206&p=1301269&hilit=BSO#p1301269

You could even just buy decent bikes at your local bicycle shop. You could support your own community doing it that way. In my city there is a used bicycle store for the community, I buy lots of used parts from them, but they also sell used bicycles that people donate to them. Then they fix them up and sell them. I am always on the hunt for shit in their store.

Those bicycle you linked to are a straight up gamble. Who knows what the quality is like. I wouldnt want to gamble on those bicycle.

Judging by those bicycle, you want a fat bike cruiser style. A surly is a nice bicycle.
https://www.pinkbike.com/buysell/2180158/

Thanks for your reply. I've been thinking about building one over buy from a company. If I'm not mistaken getting a 1000w bbshd kit and a good battery, some kind of decent bike might only cowt me around 1500$ If I were willing to build it myself. I will look into all those brands that you have suggested. Maybe I can find a good deal on a used bike.