For the same reason that why you buy most of what you own instead of say, grow everything you eat, make your own clothes and live in log cabins from trees you chop down.
It's simply much more efficient to focus on doing one thing instead of trying to cover everything. This is true on a grander scale as well. If those countries try to do a lot of the things they aren't as efficient in ultimately they'll be worse off than if they just mostly focus on something they're more efficient at AND selling them to bidders that need it more.
TradeSNS易之家呼吁广大网友遵守网络相关法律法规、严禁发布各类敏感不实信息；
同时TradeSNS易之家将严厉打击各类不法传播活动和违法有害信息，构建和谐的网络空间。