Yeah, no one want's to lock up their funds 3 days on steemit with the market available to trade instantly, so that Convert to Steem option is useless. This isn't the bank where we're all in a financial straight-jacket getting interrogated and waiting for them to let us, MAYBE, do what we want with our money.
Most likely it's there for legacy reasons from the beginning of the platform. Just like the auto-upvote yourself check box is outdated but still there. [the "I love me" checkbox!]
I actually thought to myself that the convert to steem option might be a legacy option. It makes sense