The international communities do recognize the independence of countries--Timor-Leste and South Sudan are two countries that declared independence in the 21st century. However, when independence isn't mutually recognized by the former parent country, you get reluctance from the wider community to recognize it. Kosovo, Palestine, Taiwan, and Western Sahara are functionally states with recognition issues best summed up as "it's complicated."

The next clade of states are those formed during civil wars or other breakdowns of states, such as Somaliland or competing governments in Libya and Yemen. There's a preference by the international community to stitch countries back together rather than admit their dissolution. Partially, it should be recognized that states fracturing up this way tend not to produce stability--turning internal administrative boundaries into international boundaries makes life very bad for people on the wrong side of the border, and there's usually no easy solution to that. Partially, too, there's a desire to discourage wars. For similar reasons, there's also a clutch of unrecognized states that are essentially frozen conflicts being perpetuated by a third party (not uncoincidentally, most of these are in the former Soviet Union--see previous note about international borders).

The final clutch of stuff is the performative micronation (cases like the state at question here), which is almost invariably about trying to evade the authority of existing states. And that should immediately explain why there is very little desire on the part of those states to sanction their existence.