730 lbs × 0.02 (2% of Body Weight) = 14.6 lb/day
21 lb/day is like 2.8% of body weight/day. Thats a good bit of feed for a 730 lb steer.
First, get with an experienced feeder and determine how you want your steer to turn out at his end point. Keep in mind, you want your steer to grow. The goal at this point is growth, not to get him conditioned. You should not have problems getting him conditioned since you won't be fighting the summer heat, so save that for later. Feeding your steer 2lbs of STABILIZED rice bran per day will put on conditioning in a hurry.
Tweaking your ration, and making certain it is balanced can probably solve your problems. All steers dont perform well on free choice hay either. There is no "cook book" way to feeding a steer when it comes to feeding him to look his best at his end point. There are methods to managing a steer to optimize results based on their natural instincts, typical behaviors, and body make up (digestion, rumen function, etc.).
There is a lot of information available these days. Research the different feedstuffs and learn the advantages/disadvantages of feeding each. Learn about energy, TDN, protein vs. fiber, feeding mineral, etc.
My advice to you is;
1st - analyze, study your steer and get a visual of how you feel he should look at his end point
2nd - study your ration (with help) and see if its balanced correctly to "grow" your steer. If not tweak it, or select a commercial ration that will do the job.
3rd - one you get your ration squared away, feed your steer what he can clean up, and watch his manure..... A good feeder pays attention to that.... Hint.... Hint... Gradually increase over time as he starts to consume more. Feed a good mineral, good hay and clean water. Instead of free choice hay, maybe controlling how much is the ticket.
4th - Once he is eating consistently, then supplement your ration as needed when needed, with his endpoint in mind.
Good Luck