Not just marketing. Carbon fibre and weight reduction can get very expensive.
Of course, you pretty quickly hit diminishing returns, and most people don't actually need that for a short weekend trip.
But it can make sense to spend a few thousand on a bike, if you're using it to commute or you use it for work (deliveries, etc.).
price of motorcycles. You can drop £10k on road bike or mountain bike, and still not really get top of the range. Look up what kind of motorcycle you can get for that money and then make a value judgement .
Don't know much about bikes, but I remember reading the story of someone who had bought something insane. Think a high end ducati. Anyway, he was complaining about how it overheated and/or got to hot at traffic lights. Someone pointed out it wasn't designed to idle at a traffic light or cruise highway speeds. He was driving it too slowly for it to cool the engine properly. He'd bought a bike that was designed to go fast, only to find out it wasn't actually that good at riding around at relatively slow speeds.
Don't know if that's true, but it does illustrate that more expensive isn't always necessarily a better choice for an individual user.