The only reason it is the first thing mentioned is because it is usually very important. I have just returned from Colorado Springs where I have been doing a little mountain flying.
The field I flew from - Meadowlake - has a unicom with automated "ATIS" and it always gives a caution about the density altitude. As the field is at 6,800 above sea level, performance is almost always critical even with a 6,000 foot runway, when the DA is almost 9,000 feet.
Last Thursday we flew 2 up, restricted our fuel to less than half tanks in a 172 R and did a lot of gradual climbing to get to just under 12,000 to safely circle Pikes Peak, 14,100.
Denver is at over 5,000 feet and much of the countryside around is flat but 9,000 above sea level (no QFE then !!!)
Because in our cool climate and low altitudes (my home field is 81 Ft AMSL) we generally don't need to worry about density Alt, doesn't men that on the wrong day it isn't out there waiting for us.