About Turkish Language Reform, there are many to say as to its motivation asked but I want to say a few.
First of all, it wasn’t actually about “purification” of Turkish lexicon. Before Reform, the official use of language was so distinct from public use that there wasn’t even a consensus on how to spell some of official words. Almost entire phrases in an Ottoman document were meaningless to common Turkish speaker’s ears. Many of the words were long out of their primary meaning and searching in Arabic language in the need of loanwords or generic words was almost an instinct. Year by year, Turkish official language was splitting away from its native speakers by the hands of officials and Istanbul bureaucracy.
Second, one shouldn’t script a language with 8 vowels like Turkish using Arabic abjad. It creates a mess. Distinctly articulated common words like “kul” (slave), “kül” (ash), “kol” (arm), “kaval” (flute-pipe) were written same, قول, in Ottoman scripture. Even before Republican era, some Ottoman intelligentsia noted the nonsense and made proposals for a reformation of alphabet, which all never actualized.
Third, public use of Turkish language hasn’t throughly changed since 14th century. We see it at numerous records of folk conversations by European travelers in Anatolia. Turkish speakers of Anatolia didn’t see a Great Vowel Shift like English language got through. The reform, also, didn’t even touch a thing in folk language. It just abolished traditional Ottoman use and standardized Constantinopolitan Turkish accent. Thus, Turkish Language Reform was actually a reform on official use of language. An ordinary Turkish citizen in 2018 doesn’t understand a 1925 speech by Ataturk but, aside a group of well-educated upper class, any ordinary Turkish citizen of 1920s couldn’t understand it too.
If you’re a common literary person, a language reform is nothing but a torment to you. The state had to convince bureaucracy for the requirement. So, based on the worldwide trend of local nationalisms, a “Turkification” in language has been advertised. The reform period has been depicted as a drama of “pressured, looked-down, productive Turkish language breaking its chains of ages”. The sudden boost of literacy was considered a positive feedback and many of officers adapted the alphabet easily since had they taken mandatory French classes in classical Ottoman education. The reform was seen mainly successful. Later, both nationalist and leftist parties supported and interiorized the reform into their agendas indicating it to be a key struggle for society and campaign of education.