It should be the business of the writer, and no one else, as to handling their tax situation, if they have one at all. The IRS harasses business to act as unpaid government informants and surrogate collection enforcers on their behalf. The US tax system is based on this kind of admin shakedown to make third parties document transaction activity in a manner that presumptively characterizes it as taxable (whether it is or not), then uses this paper trail to create a phantom, but equitable case for liability. This allows them to make a assessment that they can hound people with.
This is why you should submit stealth identities and profiles to such sites, and limit you earnings to under $600 per account, if you don't want to feed the tax beast and their magic 'paperwork=liability' system. Fight phantom tax liability with phantom docs. Better, spread your writing gigs across 10-15 sites on this basis, so. you aren't devastated when one site withholds funds from you.