What Sadilsor said.
I have 3 chain drive bikes. All chains and sprockets are over 2 years old. All have 15000+ miles on them. None need replacing. sees a lot of dirt and fairly hard use.... The chain on my Blackbird is at least 14 years old (on it when I bought it in 08) and has 30K+ miles.
I agree, you are not going to need to replace chains and sprockets if you don't ride each individual bike very much. which is why I said "today's chains are fine if you are not going to ride a lot of miles". If you have ONE bike, and it's chain drive, and you ride a lot on that ONE bike, you tend to wear them out fairly quickly. Since I retired in 2013 I have averaged 302 days of riding and 22,552 miles per year. I'm at 84 days and 4,200 miles already this year, and it's not "riding season" yet. Three trips are planned for later this year. If I run my average miles on my current chain drive bike, my chain and sprockets won't go 18 months much less 14 years. Of course if you spread your yearly mileage out over 3 or 4 motorcycles, each one will last longer, but in the end you will still have to eventually replace 3 or 4 sets of chains and sprockets, just as if you had run up the same amount of accumulative miles on ONE bike.
The leader on the mileage tracker is already at 15,000 miles this year, so a chain lasting 30,000 miles would make it maybe 6 or 7 months for him before he had to replace everything. Each year the top 5 or 6 on the mileage tracker run up enough miles to go thru a set of chain and sprockets in one year. EdIt: If they ran those miles on ONE chain drive motorcycle.
I guess one would have to consider how many miles that they consider riding a lot. I've heard guys brag that they ride a lot of miles a year when they ride 12,000 miles per season. Compared to the AVERAGE motorcyclists who rides maybe 2500 miles a year, that is indeed a lot of miles. A lot of miles to me is once you start topping 20,000 miles a year. YMMV (see what I did there? lol)
There is a reason the premier touring bike from nearly all manufacturers comes with a shaft and not a chain.