More seriously, a couple of observations:
1. Most styles of kung fu require dedicating years of practice before one can be called skilled. Compare this to Systema or Krav Maga where one can become a killer very quickly and you can expect people with little time to train to prefer these more modern martial arts. This says nothing about the depth of these martial arts, just the way they are organized and taught. As a concrete example: one of the first block I learned in Flying White Crane Kung Fu is actually very difficult to use in a street fight. Once you're good with it though, the opponent is in a very bad situation. With Krav Maga, the first block you may learn is usually very basic, very effective to block a punch, but you get less counter-attack possibilities.
2. Most of us do not need to fight for our life so of course, martial arts are waning as a whole.
3. MMA is very popular and most Kung Fu styles are not suitable for MMA: again it takes time to become an expert and many techniques cannot be used in a MMA ring (can I put my finger in your eye? what about using pressure points while you are tackling me on the floor? can you hit the neck with a spear hand?).
4. Kung Fu masters are usually very secretive and they sometimes die with most of their knowledge, especially if they do not find someone suitable to transfer that knowledge.
5. Finally, a sibling comment mentioned youtube. Many kung fu schools hesitate to use Youtube and when they do it, they usually do not show the best they are capable of. When I was training, I remember a master asking to only capture the movements of the upper body and hide the footwork :-)