They do slow down after a bit:

Once nearing the ground, drop pods activate a drag chute (more formally termed a "Drogue Panel"[10]) formed from the upper-most panels. The chute deploys and begins to slow down the pod's descent. Once about 1 kilometre (0.62 mi) from the ground, a series of computer-controlled retrothrusters engage and rapidly decelerate the pod such that it can impact safely.

Also most (not all) drop pod deployments are used by specialized troop like ODST or spartans:

Of these, the UNSC are particularly reliant on the use of drop pods thanks to the aptly-named Orbital Drop Shock Troopers; specialised shock troops who specialise in the use of drop pods to insert behind enemy lines and conduct special missions.[7][8] Although the ODSTs are the primary users of drop pod insertions in the UNSC, both Spartans and regular Marine forces may also use them.[9]

https://www.halopedia.org/Drop_pod