Because they need to keep some gaps in the tax law to allow their friends to pay less taxes than normal people.
The US famously had a huge amount of tax law exemption just because of corruption. Nowadays you need an international setup to achieve the same, because the same old tricks have been used by many and there was enough political pressure to change it.
Some countries simply just didn't go through enough scandals of finding out how all well networked people pay almost zero taxes and therefore still have some relatively simple setups to pay little taxes.
A separate matter is countries trying to desperately attracting businesses and creating tax benefits only for wealthy expats, but not for their own people.
> Because they need to keep some gaps in the tax law to allow their friends to pay less taxes than normal people.
The self-employed in Poland provide almost 30% of total budget revenue from income tax [1]. (This statistic is somewhat dated, but I don't believe it's changed drastically since). That's a lot of "friends" and "wealthy expats".
It certainly helps the IT sector to stay globally competitive, also attracting foreign talent (hence plenty of programmers from eg. Ukraine, particularly these days).
Being self-employed has its own downsides - if anything goes south (as in, you did something terribly wrong, there's graphite on the ground, and you're held financially responsible for the outcome), you are liable down to your very last penny, in theory at least.
By comparison, if you're on a contract of employment, you're only liable up to the equivalent of your three salaries, even if your negligence has caused damages in the millions.
You are not protected by the labor law (by contrast, getting fired on an employment contract runs into plenty of legal protections should you choose to dispute it).
It makes sense to me that accepting greater responsibility - as a one-man company - gets compensated somehow, like in the form of lesser tax burdens.
The US doesn't do this. They try to make self employed vs employed by a company have the same tax rates.