Many of Nintendo's most bizarre peripherals failed because they were before their time. This, however, is not true about the Speedboard, it failed because it was a heaping pile of garbage as a concept.
Video game players get a bad rap for being lazy. The Speedboard seemed to be designed to
give people with that mindset more ammunition, as the consumer is essentially paying for an ugly piece of plastic that does nothing more than hold their controller for them. It was pushed as a revolutionary device that would allow for higher scores and quicker reaction times, yet it was no different to simply placing your control pad on a table and hacking away at the buttons.
This NES accessory bombed and it was quickly (and quietly) discontinued a couple of months after its initial release.