While the arguments are solid in terms of portability and convenience, you cannot just glance over the price issue. More often than not, price and budget will always trump any persons choice when choosing between a full PC or gaming laptop. And the price differences are big enough not to ignore. These 1080 sporting laptops all retail for nothing under R35k in SA, and arguably the same spec machine can be bought for about 25% less. That's a lot to pay for convenience. And seeing that many employers will provide laptops to employees, the convenience factor is even less of a priority when buying a system for personal use.
Then again, there are exceptions to this, and the fact that gaming laptops are becoming better and better, they do become legit options to many people for their gaming solutions.