"Abundant energy for humans" usually means that there is enough energy for all basic stuff that humans need to do. It doesn't mean there is totally unlimited amount of energy.

If you get something for free and you get rewarded greatly to use it, wouldn't you use it as much as possible?

If bitcoins worth of hundreds of millions of dollars are distributed every day, you can be sure that there are individuals and companies who want to take as much as they can. If energy is abundant, they will use it to generate electricity, mine minerals from the ground to get resources for hashing equipment and continue to do that until they hit some kind of limits.

My guess is that "abundant energy" won't so so abundant in that scenario. But of course, maybe the limitation will be caused something else, like lack of metals to build hashing equipment.