again, people already accomplish exactly this thing by posting screenshots of text. but that's less accessible, less searchable, and an overall poorer experience than letting people post actual text instead of screenshotting it first.
and if you don't personally use twitter, i'm not sure how qualified you are to judge whether or not something defeats the purpose of twitter.
I am an active Twitter user and I know what you mean by screenshots of walls of text. There is no endemic use of such modality across Twitter, with few exceptions.
I stand by the statement that Twitter moving into publishing long-form content puts it on the same pedestal with Medium and defeats the purpose of the platform. Which is OK - strategy evolves, and someone did the math that this is going to be more beneficial.
My other comments reflect my stance on their decision, but I am neither a product manager at Twitter, nor do I have any knowledge of the "whys" so take this with a boulder of salt.
and if you don't personally use twitter, i'm not sure how qualified you are to judge whether or not something defeats the purpose of twitter.