Why can't I deduct personal funds lost due to fraud?

The taking of money or property through fraud or misrepresentation is theft if it is illegal under state or local law.

Theft loss deduction limited. For tax years 2018 through 2025, if you are an individual, casualty and theft losses of personal-use property are deductible only if the losses are attributable to a federally declared disaster (federal casualty loss).

IRS Publication 547, Casualties, Disasters, and Thefts page 4 - https://www.irs.gov/pub/irs-pdf/p547.pdf#page=4

there is also a special provision for deducting casualty losses from Ponzi Schemes. TurboTax does not handle this situation.