The problem is that coin incentivizes* the use of electricity, which is a dumb thing to incentivize. Sure, we can incentivize the use of electricity, but we can also decide to incentivize something else.

A system like bitcoin but that only uses (all of) the CPU 10% of the time incentivizes a lot of cheap compute power for projects that need it. As an example. Algorithms that have similar loads to conventional software encourages more powerful general purpose computers instead of more powerful custom bitcoin ASICS.

There are much better things to incentivize.