It's also about the level of tax they will have to pay going forward, which appears to be stupendously height (at least for freelancers). It appears on par with, or even higher than, what people with regular employment often pay, in countries with elaborate and functioning social security/welfare systems. Serbia certainly does not appear to have those.
It does appear as if this government really does not want freelancing to be a viable option. Considering the recent efforts to attract foreign investments into local Serbian (tech) companies, where almost insane return-on-investments figures are being promised (of course flowing back to the foreign investors), with all kind of questionable perks (pretty much destroying any potential competition from local businesses), it's not impossible that there is an orchestrated scheme going on here.
It sadly would not be a new phenomenon if/when in Serbia a small group of shot-callers are manipulating anything and everything to just enrich themselves, by collaborating with questionable (and ultimately abusive/destructive) foreign enterprises, at the expense of Serbia's citizens and in fact the country as a whole.
But, we'll see what happens.