Because a lot of things are upside down in Arg, having the equivalent to a masters degree, and very high levels of education would not guarantee that you will be making very good money in dollar terms here. This is the reason why some professionals and scientists leave the country. The ones that remain get creative and usually have more than one job at a time. Populism and some unions caused an imbalance between professionals and workers who sometimes earn a lot more in money terms.
So when you wonder how do they do it, bare in mind that a lot of people have more than 2 jobs, or a regular job and a side project, etc.
Argentina is cheap for expats due to recent devaluation of about 100%. It is certainly not cheap for locals, earning pesos and having goods and services tied to dollar rates.
A maid or nanny are affordable, until you get sued. You need to be very aware of labor rights and how this work in Argentina. This is one of the big reasons why a lot of foreign companies are reluctant about investing here.
Some people buy nicer clothes or brand name clothes at malls, etc and they are expensive, but a much larger number buy no name clothes in smaller stores, fairs, etc. I actually got myself 4 t shirts @ 250 pesos each ( nice quality, don't shrink, etc )
Middle-middle class does not have the same mindset and expectations than their middle class peers have in the US: they rent or own their home because they inherited it mostly, they go on vacation a lot of the times sharing the cost of renting a vacation house with another family or two their friends with, or with relatives, so they split the costs. They like to go out to restaurants, but are equally happy if they can cook a nice asado at home and chill with friends. They might do the fancy restaurant thing for an anniversary, etc, but in hard times such as these, they will just go for a coffee when they go out.
We have been through so many crisis that people are used to adapting to getting less for their money.
Many single middle class people in their lat 20s or even 30s still live with their families, so they can spend some more on clothes and entertainment.
They overall quality of a lot of the goods and services that are locally produced in general is not good, but mediocre. There are many exceptions. If you talk deeply with some small industry owners, you will understand why: they do not invest, they try to profit as much as they can selling crappy stuff because they know the country is unstable, one day you get flooded with imports, the next imports are banned and you can only buy local stuff. So if the later they make money, when it turns around they all go broke ( current case scenario )
A lot of the upper middle class here are land owners, that are involved in one way or another in exports. So they buy expensive cars and properties. You also have actors, politicians, judges, sport players, narcos, and friends of those in charge of the administration, that get the chance to work for the federal administration or get juicy contracts to provide services in one way or another.
Hope I was able to shed some light.