You want to play what outside home? Do you need 200fps on some battle royale game outside home? Or do you want to play resident evil 2 at ultra settings on a 15 inch screen outside home? I dont get it. A mx150 will run everything at 720p (still good ppi for 15 inches) and deliver entertainment
I was using a generic "I".... as in, anyone who wants a gaming laptop... But I use, for instance, an Alienware 18 (it's almost 5 years old now) that has a really nice 1080p 17.3" screen. It has dual Nvidia 880m cards - which at the time was pretty much the best you could do in a laptop. Yes, it cost a crazy amount of money (mine "fell off a truck", but they retailed at about $6,000 brand new with everything maxed out), but if you wanted to game on the road, it was worth it.
Yes, buying 2 desktops with the same specs would probably have been cheaper - but sometimes you need the system to be mobile! I could take my laptop to work, a friend's place, or up to the cottage and use it... can't do that with a desktop - or at least, not without unplugging tons of stuff and carrying around everything...
In tech, size is as important as "power"... if you don't mind having something 3 feet tall, by all means, get yourself a giant tower case and cram it full of awesome

You'll certainly get more bang for your buck.... but if you want to be able to fit it in your backpack and take it with you.... you're going to have to pay for that privilege.
While 720p on a 15" screen might be good enough for most, it ISN'T good enough for everyone... Some of us want the best (or almost the best) a desktop can provide, but in mobile form.