Oh, this depends on many aspects
As mentioned above, road cars require lightness, excellent geometric structure and excellent aerodynamic performance, of course. Intensity is also important.
Let’s talk about lightness first: Lightness requires very high requirements for the material of the frame and the technical requirements for building the frame. The two mainstream materials for road cars are aluminum alloy and carbon fiber. Aluminum alloy will be based on its Different metals and proportions will have different properties, so developing an aluminum alloy that is light, strong and has good plasticity is one of the core R&D projects of the technical teams of major manufacturers. This requires investment. It is a patented technology that has been researched, especially aluminum alloy and carbon fiber. The weight of Trek's best climbing frame is only 690 grams.
We are talking about geometric structure: geometric structure must be combined with aerodynamics. Yes, the biggest enemy when riding is wind resistance. Minimizing wind resistance as much as possible is a technical issue that major manufacturers have been pursuing and developing, such as electric transformer kits and the technician-killer windbreaker TREK launched this year with purely internal wiring. Madone 9 and others are the crystallization of technology
There is also the craftsmanship, which I won’t talk about
But one thing to say here is that the mountain bike frame is not cheap...it’s just that it’s relatively cheaper than the road bike frame. Car prices are low