She can pay in installments vs the entire sum at once: https://www.irs.gov/payments/payment-plans-installment-agree...
But credit rating counts for a lot.
Even if they can prove sufficient steady income, if they don't have a good credit rating, there's a good chance they are unable to get a bank loan, credit card (or additional credit if they have a card already), and perhaps not even a small overdraft.
I can't speak for the US, but in the UK, even "payday lenders" who charge >1000% APR rates will no longer lend to someone with a poor credit rating.
On top of that, for someone who isn't used to it, and who already lives on the edge of what they can afford, "thousands", probably at high interest, is a big loan they may reasonably worry would put them into an unrecoverable debt spiral.
I am friends with a camgirl who is a prime example of this. In her case, she made a go of full-time camming, and thought she was doing well. What she didn't understand is that the site she worked for paid her as a contractor and withheld nothing. She never thought much about taxes, and all her previous jobs had withheld taxes, so she didn't pay quarterly estimated taxes. Last month, when she went to file her taxes, she realized she owed thousands. She has been struggling to pay this while other unexpected expenses mount (car repairs). She's struggling with the decision on whether to pay her taxes or her rent, and is about to become homeless.
The super irritating thing to me is that she had a gofundme setup for her friends and family to donate to help with her tax issue. The campaign was going well (close to 50% complete) but gofundme took it down and refunded all the donations. This was likely because they don't want to be associated with sex workers, and she apparently had a link to it from her cam-site page.