Using the semiconductor technology of its day, Intel's engineers weren't able to translate the design into a very efficient first implementation. Along with the lack of optimization in a premature Ada compiler, this contributed to rather slow but expensive computer systems, performing typical benchmarks at roughly 1/4 the speed of the new 80286 chip at the same clock frequency (in early 1982). This initial performance gap to the rather low-profile and low-priced 8086 line was probably the main reason why Intel's plan to replace the latter (later known as x86) with the iAPX 432 failed. Although engineers saw ways to improve a next generation design, the iAPX 432 capability architecture had now started to be regarded more as an implementation overhead rather than as the simplifying support it was intended to be
What are the stated main reasons the iAPX432 architecture failed?
The many features included resulted in a very complex processor that was difficult to manufacture. The complexity also resulted in a very slow and expensive processor which was not competitive in the market. The initial failure cast doubt on the entire approach taken to develop a new architecture, making further iterations to improve the processor more difficult.