Steemit was in need of funds and Tron was in need of an actual ecosystem with an actual community. Steemit Inc is also a very experienced team. Tron probably has a lot to gain from this purchase.

Together, TRON Foundation and Steemit Inc. will look to create further value for their users and to augment their advancements in decentralized technologies, including moving old STEEM token to a new TRON based STEEM token, giveaways to the existing TRX users with the new TRON based STEEM token, as well as a new accelerator program towards the developer community.
https://medium.com/@TronFoundation/steemit-joining-tron-ecosystem-6ad66584d0b

This is the unwise part IMO. Having focus on social media and gaming and not being general purpose makes STEEM much suited for scaling. Migrating to a general purpose blockchain just doesn't make a lot of sense.