They are rating him above average and probably think he is still ascending. The injury history is a concern.
Personally, I think investment in the oline is normally one of the sounder strategies. If they are right, but wait until there is enough body of work to confirm it so that it would be an easy consensus, the price tag goes way up.
Folks who are uncertain can always point to failed gambles, but I don't think a GM can avoid projecting and gambling. It's sunk cost now, so let's hope Beane got this one right.