I suppose it's not that surprising, there are a million invites now and it takes like 5 minutes to make a new account (not fine). Plus the fact that people make smurfs to teach their friends (like you do) so that they don't play high level matchmaking. (This is obviously fine of course!)
That Valve matchmaking is very good at this aspect actually which is quite important. Anyone who is any good at the game seems to get very quickly lifted to a much higher matchmaking level (for example the streamer Draskyl who made a smurf account yesterday because he ended up in low prio, is already playing somewhat decent players (at least not first timers)) I don't know how it manages to do it, maybe it is really clever and can see who buys a ghost scepter, BKB, how many denies you have but people I know who have smurfed (I haven't) say it doesn't take more than 4 or 5 matches to be at a similar level to before.
It's just frustrating when my friends have to be convinced to buy wards at all, and the other team is smoke ganking at the 5 minute mark. I think he averaged 15 deaths a game for the past 5 games we played together. While I was usually better than the other team, the difference was too much for me to overcome. For example, one of those games I went 9-4, and the rest of my team went a combined 1-38. Completely overmatched.