Companies buy businesses for two reasons. To gain new technology, and to get as close to a monopoly as legally possible.
To the former, blockchain technology is around in multiple and it'd be cheaper to hire developers to build a new one, or buy a blockchain not already integrated into a social network.
To the latter, if he's going to do it, he should do it now. This is a volatile site that, if it really starts taking off, won't be worth selling.
RE: Mark Zuckerberg Again for Steemit