There are several issues with that.

First and foremost. Most people’s devices are not powerful enough to make any money mining any cryptocurrency.

Also a cryptominer is not “free real state” it chugs the computer. The user would have a terrible experience trying to do anything with a cryptominer on the background.

And finally, there are many free software out there. Not everything is to be monetized. Some things should just be free. I have done plenty of free things for others to enjoy, it’s not the end of the world, quite the opposite is quite rewarding.