No one has to sign up for any growth accounts. In fact, if you know how to mine why would you?
Because of the insanely high PoS reward in combination with the uneven percentaged effect of compounding interest between poor stakers and rich stakers, high variance + no predictability because of the floating stake modifier, proportionally lower chances to find a block for stakers who don't mint 24/7, necessity to compensate for the decline in purchasing power due to hyperinflation etc.pp.