For some context, a lot of companies hire parent contract companies to hire out for a certain department. These parent companies then subcontract out to smaller companies to fill these positions. Example, USAA's Service Desk is ran by HCL, who then contracts out to other smaller companies to hire for the position.
What now ends up happening is that these smaller companies all offer various pay scales for the same job.
Now, if an employee knows this, they can immediately jump ship every 6 months, sometimes before, and start making more money. Reason being is that only the employer is obligated to fulfill the contract as the employee is not (unless stated otherwise, but that's not what we're here for). That's how a lot of tech contractors operate.
So with all that being said, I've noticed that jumping contracts is frowned upon. Even by the parent company, they view that as some weird act of treason but let's be clear, the parent companies are the ones allowing multiple smaller companies to be on the field. The best way to describe this situation is by noting the meme of the kid who sticks a branch into his bicycle wheel only to complain about a scraped knee.
Also, the main companies some times don't have a waiting period before you can apply again mostly due to then not actually handling the hiring process.