Its just like anything else. Take the roof on your house for example. A typical shingle roof will last anywhere from 12 - 20 years. A standing seam copper roof will last a couple of lifetimes. When you take a look at cost it is easy to see why not everybody has a standing seam copper roof - even though it lasts 5+ times longer than a shingle roof.

Shingle roof = $1 per sq. ft.
Copper = $15 per sq. ft.

Or what about flip flops. There's the Dollar General variety for around $2.50 that will last for 2 or 3 months depending on abuse, then there's Rainbows which might last 2 years or more.

One thing is for sure, if a boat is taken care of,it can last a very very long time. A lot of it comes down to the market and the manufacture has to provide a good product at a good price to be able to compete.

Blue's exactly correct... the market (and to a certain extent, snob appeal) sets the price and the materials used in the construction of just about everything. For example: I used to have a John Allmand 25' boat. Great boat, heavy, well made... They couldn't compete with cheaper, less well made boats. They are out of business now.