It was a failure because it was intended to become the
proprietary bus of
all x86 PC's and give IBM control over x86 clones. What it did do is show
the world that the clone makers were in charge of their own destiny and
standards (like EISA) and that the x86 platform would remain non proprietary
and not under the control of one manufacturer.
In the business world, it all comes down to the bottom line. I think
that of MCA was clearly in the black.
If MCA was such a failure, IBM would have killed it off quite quickly.