Yes but simply linking makes it more difficult to automatically censor content. Aside from the problem of redundancy (sorry, old school here, redundancy must have a reeeally good reason for me), as I have already mentioned, this would get your readers used to reading you ONLY on twitter, while by linking to an external blog your readers will already be used to read you elsewhere, in case your account suddenly disappears.
Of course I imagine that in addition to the intent to expand outward control (and let's call it aggressive "moderation"? the infamous dangerous "unfettered conversations" come back to mind ;)) of content as an alternative to blogs, there is also the intent to offer it as an alternative to long threads, which to me, however, does not seem like a good idea as well, because it is known that the average reader is more likely to read in chunks rather than deal with long text (as others have already said). Not to mention that with threads you can reply point by point, to individual tweets, which as I see it is smoother and neater.
Maybe I'm biased (that's why I started out with "I don't know") but I see it as more of a political move than a functional one, that's all.
And by the way, if one really doesn't want to think about censorial and narrative control intentions, in the least worst case scenario to me it looks like a push toward increasing the already troubling monopoly of a few giants on content, data, attention, etc.
I don't know, in times when account suspensions and/or removals for political reasons seem progressively more frequent (and arbitrary), it doesn't seem like a great idea to entrust the longer writings to them as well... It seems wiser to maintain separate blogs.