The biggest issue is the cost. I bought an $800 mountain bike for my son, which broke easily. The store told me afterwards, it was really an entry level mountain bike, and not meant for mountain biking. You really need the $1,500 bike to mountain bike (Greens and Blues). What!?
First off, they marketed it as a mountain bike. Second, it was $800. I am sorry bike industry, but the engineering and materials don't justify $800. On top of that, it cannot stand up to the trails. Bicycles have been manufactured for hundreds of years, without much substantial technology breakthroughs. They are still steel, aluminum, rubber, gears, bearings. Compare that to the engineering in a computer or car. Bikes is shiny and neat, but building them is not rocket science.
Where is the company that builds a great, reliable bike for a reasonable price? You have my business. PS...I am 6/7", and would love an XXL mountain bike with a long wheel base and long Reach.