No, it's NOT the "only" reason. As Bert pointed out, even if they had enough fuel, the delta-V is SO MUCH SMALLER than the orbital rate, that it would take a decaday to complete the trip, much more time than the available "consumables" in their suits. When talking about speeds per second, please multiply the number by 3600 for the per hour speed and you'll quickly see just how fast a "mere" 20 m/s velocity is. (Note it's approx 40 mph. That's highway speeds. Unless Bert and Ernie are part cheetah, they certainly can't run that fast especially with those cumbersome suits.)

Clearly, you don't understand orbital mechanics well enough to have followed a couple places where I compressed some steps. Allow me to expand. Ida's rotation period of 4.36 hours, and long axis 53.6 km give a rotation speed at the "tips" of about 17 km/hr (like any free-spinning body, over time the rotation has tumbled to maximize angular momentum -- that is, Ida tumbles like a football flying end over end after a kickoff, not like a spiral forward pass), or about 4.7 m/s. These "tips" are almost a third as far from the center of mass as Dactyl is, so orbital speed there is something like twice what it is at Dactyl's distance (very rough approximation) -- that is, Ida supplies about a quarter of the needed velocity to get into a surface-grazing orbit. A good sprint is around 10 m/s, perhaps a little more for forty of fifty meters (as opposed to a hundred). If the suit jets can't manage the remaining 5 m/s pretty promptly, they're pretty much useless (even for self-rescue in case you come unmoored from your ship unexpectedly). You might also notice I didn't say they could sprint that fast in a pressure suit, only that one could almost sprint into orbit -- looks to me like a good sprinter has 3/4 of orbital velocity, barring suit encumbrance and the much larger problem of being unable to keep feet planted in a couple milligee field.

Now, a Hohmann orbit is a minimum-energy transfer from one orbit (say, the surface-grazing one at 20 m/s and about 23.8 km radius) to another (say, Dactyl's, at around 90 km radius and 10 m/s). One characteristic of this type of orbit is that it is exactly tangent to the other two orbits at its inner and outer points (periidea and apoidea, in this case), and for low-eccentricity orbits, the Hohmann transfer has a period very close to half the sum of the two parent orbit periods (so, a Hohmann transfer from Earth orbit to Mars orbit would have a period of almost exactly 18 months, thus taking nine months for either the inward or outward leg). Once Bert and Ernie have run/jumped/jetted into a surface-grazing orbit, the delta-V required to make a Hohmann transfer to Dactyl's orbit is small (should be on the close order of 5 m/s), and the wait time

*can't* be any longer than half Dactyl's orbital period -- hence

*less than ten hours*. Once they reach Dactyl's orbit, they match velocities with a circularizing burn, which can't require as much delta-V as Dactyl's orbit speed, because they already have some velocity from their own orbit -- hence, they need

*add* less than 10 m/s. Note that their "parking" time, waiting to be in the correct position for trans-Dactyl insertion, need not exceed one orbit, or at most around nine hours, so they'll spend less than twenty hours from the time they reach one of Ida's tips (hiking thirty or so km in effective weightlessness should be no big strain, nor take a long time) until they have to worry about terminal maneuvering at Dactyl.

Now, notice that even if Bert and Ernie don't jump or run at all to start, the largest single maneuver their suit jets are required to make is about 15.3 m/s to go from one of Ida's tips to orbit, with a following one of (I think, it's been 35 years since I did the math for this transfer) less than 5 m/s and a circ burn the same as the insertion burn. This could all be greatly complicated, of course, if Dactyl's orbital plane is highly inclined relative to Ida's rotation. Fortunately for Bert and Ernie, Dacty orbits prograde and is only inclined about 8º -- there'll be more error in their burns than the correction needed to change inclination by that amount, unless Bert can find a way to let his ock directly control their suit jets (unlikely, if it doesn't have bluetooth).

Mind you, the mass driver is much more interesting, as a story, than simply using suit jets to go retrieve their shuttle and ship, and much better at giving them a weapon effective against ships when they get to Dactyl -- but I say again, if those rocket packs are good enough for tween-ship maneuvering and such, and have enough propellant to be a good match for a suit that can recycle for multiple days, the only reason the rocket packs couldn't be used for the trip is if they're already depleted from setting up the excavator and mass driver.