Carbon frame that is designed for strength and durability rather than lightness? Are there such brands who have overbuilt carbon frame that is intended to last longer? Most if not all frames nowadays seem to always talk about being lighter stiffer, but I never seen one made to be strong and last longer. I know modern carbon are probably plenty durable, but I want at least one bike that will last long so I can proudly show to my grandchildren that it was my bike 'back in the day', and still being able to ride it.
Quick Google search doesn't help.

Otherwise I had to resort on titanium.
Why produce a heavy but durable carbon frame if one can have a heavy and durable steel frame that is cheaper? Apparently there are no (mass) buyers for such technology.

The bicycle industry is mainly driven by the competitive cycling needs, whether it is good or bad for a regular consumer. The choice of frame material is driven by the material properties and many adjacent tradeoffs, such as durability/weight. The resulting product price is closer to the end of the list in competitive disciplines. The product will not be initially mass-marketed in any case, which would drive its price even higher, but who cares.

At any point in time, current technology advancements dictate the sport's favorite frame material. Movement from steel to better steel, then to aluminum alloys and then to carbon was caused by that. If tomorrow someone invents how to make a frame from weightless forcefields, it would quickly replace carbon in sport.

The consumer market is more driven by a mixture of price and fashion trends, in no particular order. What is deemed to be well sold, will be produced. What does not look like a marketable thing, will only stay at bike expos and end up in museums. Apparently there is no need for carbon frames that are heavy — there are already steel frames. Besides, what's wrong with modern consumer grade carbon anyway? Its advantages and weaknesses are well known, and, if used properly, carbon has no life length limitation.