Because it is over one mile above sea level, and thus is 'a mile high.'
5284 Feet long... not 5280
I'm assuming you are talking about on a car. All vehicles have a service life. Somewhere around 150,000 miles you can expect things to start failing. Things like thermostats, alternators, water pumps...
1.24 miles (2 kilometres)
The inagural year of Invesco Field at Mile High was 2001