why do we count our time in years?

In another one of my musings, I wondered why we measure our time in years. Sure, days make sense because it's an easily observable naturally occuring phenomenon.
Years may also make sense because they enable us to bundle a larger period of time in repeatable bundles (in terms of seasonal variations).
But convenience apart, who do we attach so much emotional significance to the duration of one year? Why do we celebrate birthdays, anniversaries, new years, etc? Why do we mourn death anniversaries? Does it make any difference to us where the earth was around the sun when this event happened in the past? Not really. But we still wait until the earth is in roughly the same position around the sun to celebrate it?
I think a cooler measure would be 1000s of days past since the incident. Or if one were to wish to delink from the earth's movement, perhaps one should count in seconds, or in billions of seconds.
Wouldn't it be cool to say "Woohoo - today I am 10,000 days old!!" or "I am due to move into move into my 11th billion seconds!".
Definitely seems like a better idea than linking emotions to the orbit of the Earth around the Sun.