Because cryptocurrency mining is now one of the biggest contributors to climate change. It is killing the planet. It is a moral imperiative to shut it down by any means necessary.
You should of course make your own judgments, but many people do not consider that a good tradeoff.
Unlike actual people mining farms can be placed right next to power source so it's easier to use Nuclear / Wind / Solar / Hydro for such purposes.
While electricity transportation is an issue, it's not a huge one compared to the likes of storage and actually having something generating electricity. And, as it turns out, a lot of the mining farms just use coal (https://decrypt.co/43848/why-bitcoin-miners-dont-use-more-re...), with only around 40% of the energy coming from renewables. Even if they were only using renewables, it's still not zero carbon, since renewables also need to be built & since the total power consumption is increased, older coal plants might be used for longer.
For something, where the economic value is comparatively low.
That's 0.1% of total CO2 emissions per year (https://ourworldindata.org/grapher/annual-co-emissions-by-re...) and 0.074% of global CO2eq (https://ourworldindata.org/emissions-by-sector).
I'd probably agree that this is still pretty high for what amount to digital hording.
On the other hand the seccond most popular blockchain Ethereum is estimated at half the energy consumption (https://digiconomist.net/ethereum-energy-consumption), has a plan to move to proof of stake and has a lot more economic value.
The space is still new and bitcoin has first mover's advantage, name recognition and trust (most hashrate, most reviewed codebase, etc).
Out of total energy production that's closer to 0.07% (~170,000 TWh in 2019 https://ourworldindata.org/grapher/global-energy-substitutio...).
https://ourworldindata.org/grapher/global-energy-substitutio... puts the latest number at 173,340 TWh in 2019. This is an underestimate for the current value as energy consumption has been increasing.
https://cbeci.org/ estimates the annualised consumption based on a 7 day moving average of 120.87 TWh for bitcoin. To be generous let's assume all cryptocurrency mining is double that for 241.74 TWh.
That's only 0.14% of the total energy production, a lot of which comes from renuables (abundant cheap electricity means more profits for miners).
Even if you assume the worst case of 1100 gCO2eq/kWh (https://www.parliament.uk/globalassets/documents/post/postpn...) that's 265.914 Million Tonnes and https://ourworldindata.org/grapher/annual-co2-emissions-per-... shows the 2019 value at 36.44 Billion Tonnes
That's a grave overestimate of 0.73% assuming the most pollution energy production and even then it doesn't even compare to any other sector: https://ourworldindata.org/emissions-by-sector
Right here it says `20 863 TWh` which is nearly 10 times your worst case.
It's huge for pushing numbers around, but hardly "one of the biggest contributions".
What Nvidia is doing is like a dad making his kids share their sweets in a 50:50 ratio by taking advantage of the fact that one of his kids has a peanut allergy and the other has a walnut allergy and therefore 50% of the sweets contain peanuts and the other 50% walnuts.