Indeed, "There are very few people that are equipped financially and psychologically to handle the ups and downs of gambling for a living".

Nearly all long term profitable sports bettors I know use very similar bankroll management.
The main issue for small casual players is that it's actually quite boring, which defeats their purpose. You need to have a lot to win a little instead of having a little to win a lot. This gives the books a huge edge as it's only a matter of time before anyone who plays without proper bankroll management will get wiped out even if they take bets with an expected profit.