Like Mary said, episodes in Spain have an expected run-time and outside Spain have another. According to Vertele (I'm linking the same article, but translated), Netflix adapted the series to the international market, and if you stream from within Spain, you will get the original 9 70m episodes.
Apart from exceptions like "La catedral del mar" and series produced by paid stations, it's unusual to find productions in Spain with episodes of 40-50 minutes. The opposite happens in foreign countries, where such is the norm.
This difference has made Netflix take measures with regards to "La casa de papel" from Antena 3 and which the streaming platform includes in its national and international catalog. In Spain, the episodes remain with the same duration, but if we stream from other countries, such is not the case.
As stated by Sensacine, Netflix shortened the duration of the first 9 chapters to 40 minutes. So, the first season now has 13 episodes, not the original 9 from Atresmedia.
With the second season scheduled for April, this measure has the goal of adapting the series to the international marked. Furthermore, the plot is not affected, since the joined duration of all episodes remains the same in and our of Spain.
As to why Netflix cares for this specific show and not others, I believe it's simply because other shows (namely american shows) are ready for international markets from the get-go. Being english, producers choose their run-time and it's their creative decision. "La casa de papel" already struggles with the language barrier, and Netflix most likely tries to bridge the gap by standardizing episode lengths.