For a good reason – they are not an economically viable or a sensible environmental alternative. Sure, for replacement of single use plastics such as using metal straws instead of plastic – that makes sense. But a scoop or shaker that will be used literally thousands of times in its lifespan – there’s no real case for them.
Many people will tell you that steel is an environmentally better option as it only releases 1.83 tonnes of CO2 per tonne of steel – this is simply because the carbon content of steel is very low and a gross distortion of the actual energy needed.
What they don’t factor in is the energy consumption required to get the raw steel smelted and then repeated to produce the sheet steel for moulding - the production of steel is highly energy intensive.
Petroleum based plastics are much higher CO2 polluters because you literally have to burn 3 times the amount of oil to produce a desired amount of plastic - but the production process itself uses much less energy - Bioplastics on the other hand are much less of everything.
Putting that into real terms in this context, If you were to take a part made from steel and compare it to the same part made from plastic, the plastic part could be up to 6 times lighter – negating the difference in its production emissions across the whole end to end production and delivery process many times over.
Stamford University performed a study that concluded if the US switched all plastic production to bioplastic instead of fossil fuel based, the total CO2 output for the country would drop by more than 20% - exceeding the targets of the Paris Climate Agreement.