I heard about this man, definitely a fascinating story to learn about. But the edition into the standard Czech is no surprise, despite not being necessary (most probably). What is even worse: translations between Czech and Slovak. The Slovak natives sometimes get something in Czech, when their publishers don't want to bother for a smaller market. We don't. It is also surprisingly uncommon to find Slovak books regularly in the czech bookshops, despite the natives being our hugest minority.William Camden wrote:https://en.wikipedia.org/wiki/Adolf_Burger
A Slovak Jew who worked on a money counterfeiting operation for the Germans while a prisoner in a concentration camp. He wrote a book about it after the war. It seems his manuscript was written in a mixture of Slovak and Czech, and the publishers edited it into standard Czech.
I think the generation of Adolf Burger may have been much more used to the Slovak-Czech hybrid. Czechoslovakia was one country, with much more intertwined media market, with more mobility of some groups of people (as far as I know, it was far from uncommon to pass the several years of the obligatory army training in the other region), and with more individual sense of belonging to the whole Czechoslovakia. It was a country based on local patriotism. It was not exactly a national country, despite being created in their era.
We cannot compare the use of the Cz-Sk hybrid back then and now. Now, there are two countries, each has an official language with a standard regulated by its own institution, each has its own media market (no matter how often it makes little sense), its own politics and economy, its own schools (even though lots and lots of slovaks go to the Czech Republic). It is definitely possible to spend life "monolingual" now, while it was not so before the 1992.
I find it rather noteworthy though, that the Cz-Sk hybrid seems to be more palatable to learners than an Es-It or Es-Fr hybrid. Or perhaps we should look at more closely related languages. Would you be more or less reluctant to speak an Es-Catalan hybrid?