Just another step on the euphemism treadmill honestly. And less accurate. Idk what's wrong with saying a country is developing or undeveloped, its much less ambiguous than global south or third world, when 99% of the time what youre trying to say is that the country lacks infrastructure, economic development, and law and order.
Imo "Global South" is actually the most problematic of the three because it implies that a country is undeveloped because of its geographic position. I.e. the implication is "if you're south of the equator, your country sucks." Any nation can move from undeveloped to developing or developing to developed, but you can't move your physical location on the map.