Because you don't want to pay the self-employment taxes of an LLC.
The rare occasion where you are forced into an LLC don't apply to me as I don't trust equal partnerships.
For me, I don't want to be forced into the FUTA, SUTA, and MBT of an s-corp. My LLC distributes all excess earnings as equity. That equity is subject to the self-employment tax. Since it is equity and not wages I don't owe federal unemployment, state unemployment, or my state modified business (payroll) tax.
If I were to go with an s-corp I'd have to pay myself a "reasonable" salary. That "reasonable" salary would be subject to withholding (which is equal to the SE tax) and it would be subject to FUTA, SUTA, and MBT. Only once my earnings exceeded the "reasonable" salary would I notice any tax savings by not paying SE tax on the dividends. Since the IRS likes to assess s-corp salaries on the high side, and the burden of proof rests on the taxpayer to prove the IRS assessment is wrong, an audit is likely to trigger a delinquency and P&I for an s-corp.
The way I look at it, unless your business makes
at least $50,000 more than you need it to, an LLC is safer from a tax standpoint.
The thing is, s-corps don't avoid SE tax, they just shift half the burden to the company which is your company, so you pay it either way.