Detechto

Many reasons but here are two-

• Amazon has a flat fee you must pay $40 a month
• Easier inventory management when you have to just make sure 1 site is right vs multiple
• When you sell out many times over, inventory management becomes a huge issue

But, that's three reasons.

How can you run a successful business if you can't even count?

/r/basicincome is an okay place to start