Because this shit is immutable (technically. as close to immutable as we have). 

If Twetch goes down, we can't recover our data/posts from here easily, but in the future, scrubbers will easily recreate Twetch from blockchain data, for any person if they want to do it. 

Anyone will be able to spin up an archived version of Twetch in the future, if it was to go down again, and could make it look exactly like this or just good enough to show the timeline from start to finish and have search functions etc..