I would guess that Udemy realizes that they cannot compete with these other sites on quality (and the other attributes you mentioned). Thus they are attempting the Pawn Shop or Dollar Store approach wherein they will (re)sell (potentially questionable) material at the lowest prices.
There are plenty of sites like lynda.com, pluralsight.com, udacity.com, coursera.com, edx.org and others that either produce directly or verify the source. Lots of colleges also put their class videos online now, itunes U is great for that.