They’re more portable, lighter and arguably perfect for media consumption on the go. Add a decent detachable keyboard and it’s all the computer quite a few people will ever need.
You're assuming that everybody that buys a tablet like this also wants/has a laptop. Many people ONLY want the tablet as a portable computer while having a more powerful desktop in their home or office
In my case I have a tablet and a laptop, but my laptop ends up staying at home 99% of the time docked and acting as a desktop. When it comes time to replace it, I'll just get a desktop and keep the tablet