Any input on why this is happening would be appreciated.
HEAT and Lack of proper compaction. (and as noted possible? corner cutting by the contractor)
Asphalt is black, if it is a 90+ degree day then the asphalt is well into the 100's. Heat will make it malleable (soft). You could tamp down the tire marks by heating them up with [propane weed burner]1 and a tamping tool. But it will probable happen again on the next hot day.
You could ask you contractor to meet you half way, See if they will come back on super hot day with steam roller at reduced rate since you feel it may not have been compacted sufficiently at the time of installation. If the contractor is not amenable to working with you then you could rent a compactor from a tool rental shop and work it a couple of times on a very hot day.
If compacted properly Will it be impervious to indentation in the future, no, not on very hot days, but it should be better.