Despite all 3 sold little less than expected, PS4 and XB1 are in their 5. year on market so they done OK numbers,
Switch just had best December of hole generation, had best year of 3 and sold more than PS4+XB1 combined in December, so 1.8m is still very good despite didnt sold 2m+ like most people expected.
360 did 1.4M in 2012, it's 7th year, and PS3 had 900k in December 2011 despite also being 5 years old, and even the Wii did about that despite it's sales having crashed down. I'm pretty sure the PS2 did better in 2005 despite being 6 years old by then.
While the platforms are aging, blaming that performance solely on age is just wrong.
However, considering how Black Friday got more and more important, the market is slowly shifting away from December sales. I think for the entire picture we would need to add both November & December figures and compare those with the other years, as buyers who bought in December in the past now buy a BF deal instead.