The ZX81 and the ZX Spectrum were interesting machines at the time, but man did they have crappy keyboards.
Perhaps with a decent keyboard, the ZX Spectrum could have stood a chance against the Commodore C64. The price of the ZX Spectrum was 175 £ ($306 at the time) and the Commodore cost $595. Of course, the C64 also had much better gfx and sound capabilities.
> It was manufactured to be as cheap as possible.
Exactly. The membrane keyboards weren't aesthetic choices, they were one of a number of compromises that were necessary to achieve the price point set by Clive Sinclair. He intuited that a sub-£200 colour computer would sell in huge quantities, and he was right. My (middle class) parents couldn't countenance the cost of a Commodore 64, but they were prepared to buy me a ZX Spectrum.
> the ZX Spectrum could have stood a chance against the Commodore C64
Isn't it kind of the other way round? When both machines were current there wre about ten ZX Spectrums sold for every Commodore 64, at least in the UK and Europe.
The Commodore 64 like the Apple II was very much a North American thing.
It was manufactured to be as cheap as possible. There were the plus editions that had much better keys.