Upwork makes you jump through code challenge hoops and competes you against people in countries where $1/hr is kingly. Doesn't exactly engender loyalty.
From another perspective, upwork gives people in low-incinr countries a chance to work for companies in high-income countries without winning a lottery and leaving their families behind.
Therefore upwork directly improves equality of opportunity in the world.
Upwork terms of service require you to funnel funds through them for 2 years, then you are free to move elsewhere. Upwork also allows for early leaving if you pay a fee of $3500 or some other number based on crazy calculations.