It's nice when someone compliments your reliability because it means they think you are dependable. Things that are known for reliability? Your best friend, sunrise, sunset and unfortunately also taxes.
The word is a new one and didn't become common until after 1850 during the Industrial Revolution. Before things were mass produced, how reliable they were was not such an issue. Interesting fact: reliability is an American word, and the Brits scoffed at its new usage.