You need a capable rig to power PC-based VR, which limits your laptop selection significantly.
The best part of enjoying VR is sharing that experience with others. Right now this hardware isn't widely available, and so you get to be the person who shares this wild new experience with everyone around you. Seeing jaws drop, hearing gasps of amazement, and occasionally catching someone as they nearly fall down when a zombie tries to take a bite out of them is half the fun of owning a VR headset right now.
For this, and several other reasons, it's understandable to not want a bulky desktop computer to power this VR experience. Unfortunately, finding a laptop with the hardware capable of powering these headsets isn't as simple as walking into Best Buy.
Only slightly more portable than a desktop
Laptops that power VR headsets do exist. There aren't many of them, and there's a great reason for this. VR-ready laptops have to have all of the hardware in them that a VR-ready desktop has, which right now means at least the equivalent of an NVIDIA GTX 970, an Intel i5-4590, and at least 8GB of RAM. The big issue in that short list is the video card. The desktop version of the GTX 970 is thicker than most laptops you'll find in a store, and that's the card you need just to meet the minimum requirements. While the laptop versions of the GTX 970 and more capable GTX 980 are certainly smaller than their desktop counterparts, they generate a considerable amount of heat when used. This means not only are the laptops with these cards in them big, they're also heavy in order to include everything needed to keep these cards cool.
The smallest laptop that can handle the Oculus Rift or HTC Vive is the Aorus X7 Pro SYNC-BW1. It's laptop that claims to be the World's Most Powerful 17-inch slim laptop while being nearly twice as heavy as just about every other laptop in this class. While it's true this laptop is just as thin as a MacBook Pro, it's also wider and deeper and much heavier. This is the small laptop, competing products get much larger. Asus decided to deal with head by offering a massive water cooler you connect to the back of their VR-ready laptop. Alienware decided they wanted something thin, and offers a big block to put more advanced video hardware in it for when you want to play something like a VR game.
Very few of these VR-ready laptops are things you're going to sling into a backpack and take to a friends house. In fact, the only thing that makes these machines more portable than a desktop is the way the monitor is so conveniently connected to the top with that fancy hinge. Calling any of these laptops portable is a little silly.
Significantly more expensive
VR-ready computers are expensive. Building a PC from scratch that can handle VR is going to set you back at least $1,200 for most reasonable builds. There's obviously some internalized cost for assembling the PC yourself and making sure you have a nice mouse and keyboard to complete the experience, Not everyone with a desktop PC needs to build from scratch, and many of the pre-made VR-ready PCs are available starting at similar price points, but it's still a considerable investment if you're starting from nothing or from something you've had for quite a while.
Looking for a laptop you can also use as a regular computer while serving your VR needs is going to cost you a great deal more than a desktop. Laptops that meet the minimum system requirements start out at around $2,000, and anything more than the minimum quickly increases to the $3,000 mark. These laptops are incredible powerhouses, to be sure, but are also on average twice as expensive as their desktop counterparts. Even if you add the cost of a very nice monitor the cost of a VR desktop, you don't come anywhere near the cost of a VR laptop right now.
Better solutions are on the way
Having a VR-ready laptop makes perfect sense. Portability is an important feature in wanting to share VR with friends, but the current solutions are mostly impractical. Between the physical and monetary setbacks, these laptops simply aren't worth it. The good news is that isn't likely to be true for very long. HP, ASUS, Razer, and several other companies have been working hard on the next generation of laptops. They're still going to be bigger than most, they're still going to be a little on the expensive side, but there's a real focus on improving upon the hulking machines that are currently available.
Waiting isn't likely to be a convenient solution for most, especially when you want to get into VR right now, but if your goal is to have something you want to last there aren't a ton of options right now. Purchasing a machine that meets the minimum system requirements isn't going to last, and with the next wave of laptops being announced over the next couple of weeks the cost of the current generation is going to start sliding down to match. What it really comes down to is how badly you want to heave a VR-ready laptop onto your shoulder in the name of fun.