Because for majority of them, CS is the only thing they can do.
They usually don't have higher education or never learned a trade or a skill.
On top of that, there are tons of players who retire, but there are only few coach/analyst positions.
Many of them, I would presume, were reckless with money and never invested or saved up, also the prize money was considerably lower than it is today.
That's why all the paycheck stealing is happening right now. They are able to convince the investor/GM/owner that they still have it (even though they themselves know they won't ever win the major trophies), and said delusional investors pour money into these orgs that never go anywhere.
I call bs on the whole 'the need for competition' take.