Reason #4: You Can Play Anything...Any Way You Want
A little game called Skyrim came out last year (okay, The Elder Scrolls V: Skyrim, c'mon, gimme a break) - it was a vast, expansive game, with a million things to do, that would take over 100 hours to do everything the developers included. That's pretty impressive. But...it wasn't enough for some people. They wanted more. They wanted to tweak the gameplay. They wanted to modify the graphics. They wanted...to battle as a character from My Little Pony. They wanted to fight Macho Man Randy Savage. And you know what? They got just that.
The current modding community is incredible. There are people working on mods for almost any game you can think of. They're improving games (fixing bugs, balancing gameplay, adding things that never even occurred to the developers), they're adding to games (new quests, characters, etc.), and they're just screwing around having fun (it's honestly easier to count how many mods for Skyrim AREN'T mods that remove everyone's clothing than the ones that are). If 100 hours of Skyrim wasn't enough for you, that's fine - you can probably squeeze another couple thousand out of the the number of mods out there.
And with platforms like the Steam Workshop, getting these mods is actually a lot simpler and smoother than the process used to be (where mods were assembled from a variety of questionable sites and could often break your game). There are even mods that are CORRECTING mistakes made by game developers (Fallout 2 was clearly released before it was fully completed - there are missing quests and bugs galore - but the "Restoration Project" fan-made mod is practically REQUIRED to get the full game experience).
Basically, the internet is pretty cool. Speaking of...
Reason #5: Holy Crap, The Internet
The internet is an incredible thing. Videogames are incredible things. Together, they are really, really incredible things.
You want to play Battlefield against 63 other people, but you don't have 63 friends at your house (along with the horrifying number of monitors/TVs/computers/consoles you'd need to fit in your house and the incomprehensible number of snacks those people are going to demand)? YOU CAN DO THAT. WITH STRANGERS. WHO WILL SWEAR AT YOU AND YELL CONSTANTLY, BUT HEY, STILL PRETTY NEAT.
You want to discuss some obscure Japanese import game that will never be released in the US and even if it was your friends would never want to discuss with you? YOU CAN DO THAT, TOO. HELL, YOU'D HAVE TROUBLE NOT DOING THAT, ACTUALLY. The internet connects people that would otherwise never be able to find each other, and allows them to communicate instantaneously.
The capabilities of the internet and videogames is virtually unlimited, and so vast it's a key factor in nearly every item on this list, but the social/interaction aspect is a very important piece of the puzzle. You can co-op a campaign with a total stranger. You can play multiplayer against anyone. You can discuss games, rumors, swap terrible memes, and create communities that exist solely between wires. You can collaborate and make games with people you'll never meet in the real world. You can visit videogame comedy websites and click the "Like" button at the bottom of articles. You can try to subtly convince other internet users to promote your videogame article via social media. Truly, the possibilities are endless.