Why isn't PPP given due importance? A unit of money in Country X may buy far more goods in Country Y than in the former. But Country X prides in calling itself a larger economy and a more prosperous entity.
As money is just a social construct created as a substitute to represent the value of goods and thus is useless by itself : How can mere money, such as GDP be given more importance and atfention than its PPP counterpart ?
Nominal GDP is often more quoted in media and in politics than the GDP in PPP, but that doesn't make it be less important. In fact, as stated by 1muflon1 on the comments, economists typically like to measure differences between comparable things, so when comparing GDPs there are usual corrections done on purchasing power parity, as well as inflation. 

The PPP indicator has been present in literature for a long time, mentioned in the early 1500's, and translated to modern terms since 1918. It's regularly calculated by international bodies (such as the UN under it's International Comparison Programme). 

The GDP PPP is also regularly used in real life by institutions such as the OECD, IMF and World Bank to make recommendations on economic policy, and by traders to better assess when stocks and currencies might be under- or over-valued. This article on investopedia provides a concise overview.