Agreed, we need larger denomination notes to keep cash usable. Despite decades of inflation the largest notes printed are $100 and it has been that way since 1969. Even $500 note doesn't get us back to buying power parity (it's about $800 btw).
That law was passed in 1970. The amount hasn't been adjusted since then. It would approach $80,000 today if it had been indexed for inflation.
Don't know about you, but I don't foresee anyone sponsoring legislation to relax these reporting requirements, or otherwise making it easier to conduct private cash transactions with anything but toy amounts of money.