Sails have several major downsides, most notably they take up a lot of deck space and cause a boat to tilt to the side. If you’re regularly sailing long distances it’s much faster but top speed isn’t that big of a deal when your living on the boat full time.
Other options like kites and wind turbines can work well but they all all significant upfront costs as well as ongoing maintenance issues. Spending that same money on a bigger boat gets you much more space, and of course a generator can give you redundancy or higher top speeds.
This is a net positive. The alternative is to roll back and forth with the waves. It’s much nicer with the sail up and ata bit of a heel.
Also, just to throw this in, one of the world cruising sailing couples which wrote for the magazines switched to a diesel powered boat as they aged and found that they spent less of fuel than they had on new sails. Sails are consumables if you care about performance.
Your point on the diesels still stands. Properly designed cats are unsinkable and don't readily capsize, but not weathering a storm is worth every penny invested in diesels. Besides one needs them in marinas anyway.
Electrical engines are more and more becoming a thing, especially for sail boats, where they server more for harbor and anchoring than covering distances.
Racers use very thin, light, and stiff sails made from mylar or similar materials. They are typically very expensive and want to be changed as often as possible, at least once every racing season. Modern small pleasure yacht cruising sails "canvas" is laminated polyester, aka dacron, which is far thicker, more durable, springier, and more common than mylar.
It's an interesting question, where does the wear come from. But sails are a very active part of the boat; every tack is going to drag the sail across the deck of the boat, rub against fittings. When a sail luffs, head-to-wind it's whipping around with the weight of the sheets (control lines), and then when you're taking the sail down it's getting folded (best case) or stuffed into a bag (worst case) [EDIT: some sail materials like being shoved in a bag!]. And of course even when a sail is just sitting there powering the boat it's under a tremendous amount of force, which stretches it over time.
Sails do fail, and yes often by ripping in half. I've personally never heard of a sail failing at the control points (e.g. the tack of a jib), probably because those areas are heavily reinforced.
This is all spot on. Sails fail due to wear of the fabric itself, because a seam failed, from rubbing, repeated stretching and releasing (you can tell an older sail because it will bulge more as a result of this) or because it got over-stressed. Salt water obviously also doesn't help with sail fabric longevity, as does UV influence all of which will age a sail (check the color difference on spare sails that have been bagged vs the ones in use or, check the first strip of a roll-up sail to see how much that can affect the fabric).
Those areas where the sail needs to be strongest is where they are re-inforced doubling up the layers (and not just 'two', a corner can easily be 10 ply or more thick), on older boats further re-inforced with leather or heavier grades of fabric. The panels are carefully laid out so that the highest stress aligns with the warps. A large sail can be made up from many 10's of panels, which are joined in a variety of manners (glue (typically for very fast boats or as re-inforcement of stitching), stitching, sometimes ultrasonic welding for special applications). On the very high end there are even laminated custom laid out fibre pattern sails (for instance: a sandwich of Kevlar wire between two layers of bonded fabric or plastic).
At one time I worked for a competitor of North Sails, who by the way were pioneers in the digitization of sail manufacturing.
They lose their ability to hold their "shape" and become less efficient. This is primarily a concern for people that want to go as fast as possible. I've been perfectly happy with sails after 20 years of light use. I mean, I can see that they don't really have the best shape, but I'm still sailing so all is good.
You are right but it depends on the skillset and general lifestyle needs of the person. I've watched (a little) some of the sail around the world channels on YouTube and one couple moved to a performance trimaran, the guys reasoning was that he wanted to have speed to get out of the way if the weather changed.
For those that do not really stray far from the shore or who are willing to take more risk for more comfort, they use a slower boat.
Other options like kites and wind turbines can work well but they all all significant upfront costs as well as ongoing maintenance issues. Spending that same money on a bigger boat gets you much more space, and of course a generator can give you redundancy or higher top speeds.