Why do Uranus' and Pluto's moons orbit the equator? What makes a moons' inclination tilt with the rotational axis of their planet? Uranus and Pluto have their axes of rotation almost 90 degrees towards the ecliptic. But why do their moons tilt the same way?

Does it mean that their tilts were caused by passing near some external mass that affected the planet and its moons equally, rather than some planet specific process such as a comet impact or tectonics?

Mars' rotational axis tilts over time, but its moons today are spot on over its temporary equator. Earth's moon is aligned with the ecliptic and doesn't seem to care about our planetary tilt, although (or because of?) oceanic masses tugging on its tides. Exoplanets have been found that don't orbit in alignment with their star's rotation, and why would they do so billions of years after formation?
I have managed to find two hypotheses for Uranus's tilt that explain why its moons are also orbiting on a tilted plane.

The multiple impacts hypotheses lies on the fact that, if Uranus had become tilted by the force of a single large impact (as was commonly believed), then the moons should have stayed on their original plane. A corrected version of this hypothesis said that, if the accretion disc from which Uranus was forming was still around, an impact would have destroyed it and recreated it on the same place as the new equator. The moons would then have accreted from the disc on that plane. This, however, would have produced moons with retrograde motion (which is not the case for most). So the latest idea is that Uranus suffered multiple impacts, which, according to the simulations, works to produce the planetary system as we see it today. (There's another problem with this hypothesis.)

The collision-free theory (or collissionless scenario as described in the paper) proposes that Uranus could have become tilted progressively as it formed without the need to postulate an impact (or series of impacts), if it had an additional satellite and started with a large inclination (which is allowed by current models); the extra moon could have been ejected later. The simulations worked for an initial inclination of more 17 degrees and a moon of 0.01 Uranian mass and at 50 Uranian radii.