There are complicated parts of accounting, but basic expense tracking is simple and businesses would do it even if it didn’t affect their tax treatment.

If businesses couldn’t write off expenses, it would be nearly equivalent to treating the corporate income tax as a universal sales tax. This would be incredibly damaging to small businesses and benefit behemoth vertically integrated companies, which is probably the exact opposite of what you want.

If you get rid of expenses, you need to get rid of corporate income tax and either replace it with VAT or combine it with increases to personal income tax like taxing capital gains as ordinary income.

They could potentially bring a related criminal suit later. I’m not an attorney, and there are a lot of specific rules about, but the stakes are lower in a civil case (i.e. no prison) and the burden of proof is easier, so you can more easily prove things or get the defense to admit things in a civil case that can sometimes make a criminal case easier.

Even if you can’t cite the civil case from the criminal case, just the fact that the civil case ruled one way gives the prosecution confidence to commit to a criminal case and leverage if they negotiate a settlement.