For the last 10 years, maybe 20 years, there has really been nowhere else to put your money. Interest rates are the pits, international has been mostly awful, etc. It came down to the market or the mattress, pick which you want to put your money in. Maybe more people will start choosing to stuff their mattresses with cash but short of that, still not sure what a reasonable alternative investment is in this current environment.
Investments in stock also help fuel the economy. There’s a reason companies go public to raise money. Everything in life has some risk. I would rather take a calculated risk than to have little to no possibility of growing my financial worth.