Madjak’s hit the nail on the head. It’s a common perception that you’ll save money by switching to a bike, and while it’s true that you MIGHT save money by SWITCHING to a bike, most people are really ADDING a bike.
The fact is that, especially if you’re a younger guy/gal, the cost of insurance alone can make it more expensive to ride than drive. My first year of motorcycle insurance cost me $1700+. Add in gear and you’re up at least another $1000 (if you buy new). Add in the bike, the maintenance, the gas, etc. and you’re rocking a good sum. If you already have a car and it’s not an F-350 super-duty, there’s almost no chance that you’ll save money when adding a bike.
As far as bike lifespan goes, a well-maintained, well-treated bike can last around 50-60K miles, with exceptional machines lasting even longer. They definitely don’t have the lifespan of cars, but you’ll still get a good number of years out of one, especially given the lower amount of money involved.