Best remember that compared to today, there hardly was a market place till late nineties. 70s and early 80s were dominated by hardware enthusiast, 80s game software and a nerdy minority, business PCs had little momentum till late 80s and 90s. All this time, the market was flooded with different types of mutually incompatible micro computers. After DOS compatible PC gained momentum, the only company still (barely) standing was Apple, and it ultimately adopted comorbidity PC hardware too.

So I think the reason Acorn (and Commodore, Sinclair, Amstrad, RadioShack as well as Sun, DEC and SGI) went belly up is primarily that while the market was growing, there simply wasn't enough space in the market to compete with wintel dominance.