Two options:

A) You can play a game at your actual skill level, which requires your team to communicate effectively and play together. This requires someone to take the lead and coordinate the other players. That just doesn't happen in drop in games. It is incredibly not-fun and frustrating to be playing decently yourself, but be anchored by incompetent team members. You get guys who want to play their own way, or just aren't interested in "taking orders". Plenty of arrogant dudes that won't listen to someone that is a lower rank.

B) Play at a level where you can essentially carry your entire team to victory because your skill level is so much higher than the enemy. You get to fuck up a bunch of newbs and win the game, while your team mates are drooling at spawn.

B is definitely more fun. Especially when the people smurfing can get their fix of A in an organised match with an organised team, outside of match making.

Can't really tell for CS:GO but in League of Legends, good players create smurfs all the time and the motivation is usually to prove yourself and/or other people (e.g. Twitch viewers, Reddit) that you can keep a very high winrate and reach the top 1% in a few weeks. Sometimes it comes with an extra challenge like playing only the same champion.

> just destroying a bunch of new players? Surely that must get boring after a while?

Smurfs never play more than 4 or 5 games versus new players. The matchmaking system doesn't match a guy who has 100% winrate over his 20 first games with a guy who has only 30-50%.

If you play with a friend who has a low rank, it is much easier to create a free now account (that will start in a low skill group) than it is to obtain one for them which is already in a higher skill group. Not saying it is a good thing to do, but it is another reason why you'd find better players in lower skill matches.

And yet plenty of people will do it constantly. Apparently there are some gaming communities (I've heard this of China) where using cheats in multiplayer games is routine. The goal is to win, it doesn't matter how.

It's more relaxing than having to focus 100% to play on your maximum skill... Also you can play with your friends that are on a lower level. And when I do it I try to keep a 1:1 kill/death ratio so it doesn't get completely unfair for the enemy team.