Maybe I don’t fully appreciate the situation. I have known some German freelancers be stuck, unable to afford to start a business. However without a business the freelancers clients will be seen as participating in disguised employment. Same goes for issues the OP cites like personal liability, etc. In the US, business licenses are relatively easily obtained to protect individuals. It would seem to benefit society to encourage new ventures. Though this is perhaps my American biases. I’m sure I’m misunderstanding something.
Short answer: they don't.
Longer answer: countries in Europe don't want some guy opening a business out of his garage. They want somebody with fat stacks of cash who will be able to afford to pay high fees and taxes right from the start and then pay some more when/if his business actually makes revenue/profit.
Things are slowly changing, especially in the smaller economies, but change is slow.
At least in the Nordics starting up an LLC equivalent costs around 100$ in registration fees and takes about an hour (plus a week or so waiting time). Of course, you’ll need the initial capital. In Sweden it’s SEK25000/$2500.
Which is quite reasonable compared to say Germany or Switzerland (or hell, even Croatia) but still not $0 like in the USA.
It makes absolute no sense to setup a company just to check if your idea works.
In the case of OnlineOrNot (https://onlineornot.com) - I just used my name. It hasn't stopped people signing up and paying me.
Wait until you actually have a business, though.