Bitcoin is pretty much explicitly designed to use as much electricity as the market will allow, without becoming any more useful. If you removed 99% of the miners from the current system, Bitcoin will still be exactly the same - it won't be any faster or slower, and the same number of transactions will flow through. The cost of electricity serves only as a lower bound on the expected value of a coin.

Neural nets on the other hand generally show more capability as you add more compute power. There's a point where it's less valuable than the cost increase, so people don't do more than that, but it isn't constant value like Bitcoin.