Saying you make a good living on a $50k account in a first world country implies you're getting at least 100% pre-tax returns annually. Not impossible but I would not like to be in that situation for years on end; a multitude of things can happen that suddenly hamper your ability to hit that fairly high lower bound a particular year. Arguably, it's absurd to not scale such an account unless you're on absolutely tiny liquidity, e.g. microc[r]ap stock - but that doesn't change the incredibly risky proposition it is to trade a $50k account for a living.
Account = part of net worth available for investing and trading above, otherwise we are comparing apples and oranges where someone with $1 million in long term stock puts $50k into a trading account. If that $50k is part of a much larger available reserve capital that completely changes the discussion.