Spark plugs, like all car parts, are available in different lifetime spans. Some are more economical with a shorter life span. While others are of higher quality and last longer.
Of course, pricing follows suit. Sometimes money is a factor when installing spark plugs. So, you may opt for a lower quality spark plug that is also less expensive.
At other times, you may opt for a high-quality spark plug so that the life expectancy is higher.
For more information on spark plugs and the different options for replacement, go to: