Purely my opinion, but I think Ballard is simply trying to get a team friendly deal in the "now", and is probably very OK with riding out 2020 too. Could be wrong though. Given our cap situation, they may have factored him into the equation and think they can afford things if they are covered in certain aspects of the deal.
I do think however that the team has most of the leverage.
-He's not top 10 in yards from scrimmage, and is somewhat an under the radar guy
-He might be seen by some as single threaded (lacks pass game production)
-He's in a contract year, so needs to perform well regardless
-He'd get a substantial raise a year early
-An extension now would provide insurance to an extent from injury in 2020
-He's got a great OL, and will roll the dice effectively in the FA market next year
-I'm simply not convinced a lot of teams will be willing to back a truck up for him regardless.