we came up with somthing better. Like the Bradley IFV, the M3A3, or even my favorit the Stryker.
All are fast, have better armour, and better armerments then the Halftrack. The Halftrack was always vonerable to mines. With the creation of the MRAP it could have been the one to replace the Haltrack. It was perhaps the M113 AFV that replace the Halftrack.
The overall reason why the Halftrack whent out of fashion is because the world around it were finding better ways to destroy it.
Wheel or tracked all vehicles are vulnerable to IED and mine not just the old half track.
As a new design MRAP, a half track has its advantages and disadvantages, like most vehicles there are compromises. Wheeled vehicles have a higher ground pressure footprint compared to tracked vehicles; the M1 Abrams MBT weighs in at about 60 odd tonnes and has an average ground pressure of 15PSI (100KPA) tyres air pressure is approximately equal to average ground pressure, most heavy truck tyres depending if they are single or dual tyres have pressure up to around 125PSI (861KPA).
Most MRAP or Infantry Mobility Vehicles (IMV) has a monocoque or v shaped hull a technique the structure using the cabins exterior for structure support, it does not have a chassis to sit on thus a well thought out design protects not only the occupants but the vital parts such as the motor and driveline.
The benefits of the of the half track is its ability to drive and steer like a normal vehicle but has the load carry capacity and off-road ability of a dedicated tracked vehicle, not all situation would require a half track but with the situation in Afghanistan where wheeled vehicle are having trouble with the substandard road network a halftrack has the ability to go where wheeled vehicles will not.