A lot of people here say that it's very rare to spend this much money in cash for legitimate purposes as though that is some universal rule and not a cultural happenstance. I'm currently holidaying in Japan and here it is quite common to make large cash transactions and settle things in person with paper money that couldn't be settled easily that way in my home country of the Netherlands. I actually prefer the Japanese system, since digital transactions often fail; it was only a few days ago that I had to try two different credit cards and two different paypal accounts to make a payment for a flight go through, for instance. I really don't understand people who harp on about the reliability of the traditional finance system (also comes up a lot in discussions re: cryptocurrencies), since that is absolutely not my experience nor the experience of people I have personally spoken to.
This is just a side show to the real issue however, the issue of rights. Our rights are something that limits the power of the government, that protects us from the government. It is not immediately obvious that we should need rights - in well-functioning societies like the EU, the government is overall a benevolent entity, using its power to aid citizens and protect them from bad actors. We give power to the government because it is good to us, so from a first-order evaluation, limiting the government's power seems counterproductive. Yet we know from thousands of years of experience in statecraft that things do not pan out this way. Governments make mistakes. The whole of the government can be good while parts of it are bad. The government can be good at one time, and then turn bad at a later time. The government is often good to most people while being bad to some, and these people are often the marginalized and invisible.
Digital transaction afford the government (and other powerful actors in the system) two important powers: surveillance and the ability to freeze or confiscate assets. Especially the freezing of assets is devastating when done to individuals. And these things can and do happen illegitimately. Unethical mass surveillance and the freezing of assets of protestors, journalists and other political undesireables is not a theoretical possibility but a real reality. We are lucky that in the west this is mostly limited to canary-in-the-coalmine people on the margins, people whose speech is so extreme that few of us can find it in themselves to feel sympathy for them. But it doesn't take much democratic backsliding for things to get much worse. I think it's important for us all to really internalize the fact that politics does not always move in the direction of freedom and progress; things do regress, as recent history should have made more than clear to us all. We need backstops, ways for people to live lives at odds with the government. You can't live in modern society without being able to transact.
Make no mistake, by the way; these kinds of laws very much do lead to the end of cash. These kinds of laws (and laws in general, actually) tend to only get stronger, seldom weaker. Even just leaving this law on the books without doing anything else slowly squeezes the noose tighter. Ten thousand euros today are worth only about half as much as ten thousand euros thirty years ago. I am personally of the opinion that all laws should have an expiry date and all sums of currency in law should have automatic inflation adjustment, but that is a story for another time.