Courtesy of Neih:
^ More or less the general view going back to 2010. The "noob calls" come in to play based on the
belief that there is more to learn with infantry than other classes. A player can get on a horse or take a

x/bow and be relatively effective from the get go whereas it takes a fair amount of time to learn the nuances of infantry play in order to reach a similar level of effectiveness.
The other factor to consider is that because a number of players opt to go cav or ranged early on due to the preceding point, they don't get acclimated to infantry combat until much later. The result being that if they get caught in a melee scenario (horse is killed or they are charged/flanked by infantry while playing ranged) they die pretty quickly and "can't fight" so to speak.
Every class has its roles, it just comes down to realizing what they are how best to fulfill them. Well-rounded class understanding (with a strong infantry foundation) is the true key to Warband success and not being called a noob... unless you're being trolled (no shortage of that these days, unfortunately).