Imagine that baseball games were played using a non-discriminatory matchmaking service. So start of the "Dodgers vs Giants" game there would be a pause and then 25 "players" would materialize. Some of them would be athletes in their 20s with strong skills, some would be 40+ year old veterans who have good skills but aren't in shape, some would be 10 year old little leaguers who are very knowledgeable but inexperienced and out of shape, and some would be people who just randomly picked "play baseball" as their selected activity, not really knowing even what the rules of the game were. Then there is a "manager" who has to create a starting lineup, assign positions, and win the pennant.
Extremely frustrating.
Blizzard was working on "fixing" this by segregating selection of players into "twinks" and "non-twinks", "experienced" vs "non-experienced" and "hardcore" vs "casual" which helped but it still made for a crappy experience a lot of the time.