At WhiskyFest last week, I had a chance to try Maker's Mark at both 7yo and 19yo (along with new make and the standard). The 7yo was different but very good (remember I like MM). The 19yo had a good nose, but the palate lacked balance and was a bit woody.
They used this tasting to show why they only have the standard bottling. (Once the 101 proof bottling is gone from duty free it will not be replaced). They said they make the bourbon to a particular profile that is optimal for their style. If they released other (older) ages they would be perceived as "better" when in fact they were just different.
My personal opinion is that they would not want perception associated with a more expensive bottling to reduce the appeal of the mass produced standard bottling.
They also talked about how they rotate ageing barrels from the top to the bottom. This implies there would not be a "sweat spot" to chose from.
My opinion again... the just picked a 7 & 19yo to taste. These were not carefully selected, matured under a watchful eye, etc. So of course they were not exceptional. If they did carefully select and monitor barrels for extra aging, I think they could arrive a limited edition bottlings that would be exceptional. But this would be inconsistent with their overall marketing plan.