There can be a myriad of complex reasons for a product’s discontinuation, not necessarily at fault of the product. The word “fail” strongly implies that the product itself was to blame, when theoretically it could have been a perfect product, adored by a large market, bringing in generous profit for Apple, but was shut down because of inter or intra company politics or some other exterior influence. Not saying that that is necessarily the case here, but such things can and have happened before. So in place of the word “failed” with all its connotations, it would be all around safer to simply use the words “was discontinued”.
In any case, it’s a shame. I always thought the rMB was a product with great vision. It had a singular goal: the most portable Mac ever. And I think Apple was able to make the Macbook as portable as it was because of what they learned from the iPad. And in some ways, I think the rMB was Apple’s answer to their own iPad Pro. People who loved the super portable, fanless iPad Pro still longed for things about the Mac—such as central file management, floating windows, and mouse input with their keyboard. But Apple being Apple said, “No, some things need to stay separate.” But it’s almost as if that made them think, “Although... a super portable, fanless Mac is a good idea, and maybe what some of you want.”. So then they made the rMB.
It’s a given that for that level of portability (and presumably that price), Apple had to make sacrifices on performance and connectivity, which of course angled itself toward a more specific market. So for those who wanted the rMB to have more power or ports, the rMB just wasn’t made for them. But for those who loved the Mac experience, and had highest demands for portability and silence, and low demands on performance and connectivity (eg. writers), the rMB was the ideal device.
Were there not enough people who liked the rMB‘s trade offs? Who knows.
Maybe Apple couldn’t get the profit margin they wanted and priced the rMB into too small of a market.
Or maybe Apple had bigger plans for the iPad Pro than the rMB and saw the rMB as too competetive.
Or maybe Apple wasn’t satisfied with the performance of Intel’s M chips.
Who knows.