Amazon Mechanical Turk (https://www.mturk.com/mturk/welcome) is pretty transparent on their homepage how you can earn money. Amazon also lets you decide how much money per task you're willing to spend.

https://gengo.com/ for example has a subpage linked in the footer to attract translators https://gengo.com/translators/

The others, especially with a premium appearance, keep that more separate. I assume they created separate brands or use subcontractors and run "easy money, work from home" classifieds ads in english speaking countries to get people in.