I think Dropships have something extra added that AoW era Dropshuttles didn't have that no longer allows them to be inside something & must use a Docking Collar.

That said, a Warship has the HUGE bay doors to hold a Dropshuttle in it.

In the Tech Manual, we do have the Tech Level C item "Docking Collar" in the "AEROSPACE UNIT STRUCTURAL COSTS AND AVAILABILITY" table, costing 10,000 C-B. That could be the reason.

Other reasons could be mass and cost-related:

A Dropshuttle bay masses 11,000 tons, and can carry up to 2 Dropshuttles (each massing no more than 5 ktons), which would be ~5500 tons per Dropshuttle. A Docking Collar only needs 1000 tons per Dropship, and can handle Dropships over 5 ktons in mass. So just on a tonnage basis, you have an advantage to using Dropships.

For KF costs, I used the Strategic Operations Corr 2nd printing (wish the credits page had a date on it to reflect the last time errata was added to it) to compare a 500 kton vessel's compact core with zero Dropship capacity vs a 500 kton Jumpship core with 10 Dropship capacity. This did not include any other features, just the KF core itself.

500 kton Compact core:

`500 kton Compact core: DS Capacity = 0, Integrity = 12, Sail Mass = 55 tons`

Drive Coil 60,000,000

Initiator 25,000,000

Controller 50,000,000

Tankage 600,000

Sail 2,750,000

Charging System 500,000

Compact Core increase 555,400,000 (the above costs are multiplied by 4, and added to the prior total to get a final multiplier of 5: 4N+N = 5N)

KF Support Systems 2,000,000,000

-------------------------------------

Base cost: 2,694,250,000

Warship cost multiplier: 2

Final Warship cost: 5,388,500,000

vs

500 kton Jumpship core w/10 Dropship capacity:

`500 kton Jumpship core: DS Capacity = 10, Integrity = 10, Sail Mass = 97 tons`

Drive Coil 810,000,000

Initiator 75,000,000

Controller 50,000,000

Tankage 500,000

Sail 4,850,000

Charging System 2,500,000

Compact Core increase 0 (no need to multiply the above costs)

KF Support Systems 500,000,000

-------------------------------------

Base cost: 1,442,850,000

Jumpship cost multiplier: 1.25

Final Jumpship cost: 1,803,562,500

So in addition to being able to use Drop vessels over 5 ktons, you also have a KF core that is ~1/3 the cost for the same capability.

I am not considering scheduling in the matter, as even though it takes a KF vessel ~1 week to recharge while a Dropship or Dropshuttle could take 3 weeks to make a round trip to a planet, this is true for both compact-core Dropshuttle carriers and Jumpship core Dropship carriers. The Dropshuttle carrier would just release the Dropshuttles at the Jump point, and while the Dropshuttles headed in-system the Dropshuttle carrier would recharge and pop back to pick up another batch. Jumpships would perform the same maneuver.

I'm not so sure the cargo bay doors on a Mammoth are even large enough for a Union to enter.

Mammoth dimensions

Mass 52,000 tons

Length 277 meters

Width 277 meters

Height 170.6 meters

Union Dimensions

Mass 3,600 tons

Length 81.5 meters

Width 81.5 meters

Height 78 meters

The door on the Mammoth in the picture from the TRO is pretty big but its no where close to 80m tall compared to the height of the ship.

For a Union, using that door is not likely. But for the combat Dropships (i.e.

Achilles) you have LWH of 125m x 38m x 23m, which would be barely enough to stack 5 vertically. Of course it helps that the Achilles has about ten times the density of the Mammoth.

As to putting Dropships through the door, the Mammoth would have to be re-engineered to handle the large 'single' cargoes, instead of its normal containerized cargo. Since containerized cargo can be transferred 5* as fast as non-containerized, no regular Mammoth would want to deal with this. Hence the custom Dropship belonging to a unique mercenary unit.