The subreddit has ~65,000 weekly active users (ignoring this week), and the screenshots of "big" positions aren't that common, and often from the same accounts.

It's a bit disingenuous for people to make it seem like there's thousands of people putting their life savings and retirements into stocks - and even so, I would guess that many of the people who do claim to use "life savings" actually mean "the 10k I had in my bank savings account" because they're only 23.