According to Memory Alpha, the answer is that this ship has been recycled not once, but twice since its original appearance as a "ship hulk" in Voy: The Fight, making a second appearance in Voy: Natural Law (as an "unnamed Ledosian ship") and then finally in Enterprise as "Romulan Drone Ship".
I can't really do any better than quoting directly from the wiki article for the Drone Ship, itself drawing heavily on quotes from the Star Trek: The Official Starships Collection magazine.
The Romulan drone ship was a reuse of the chaotic space hulk from VOY:
"The Fight". This was at the behest of the ENT producers, who selected
the design from an Eden FX catalogue of all the obscure models
available to them for potential reuse. The producers thought the reuse
of the chaotic space hulk could be justified because its previous
appearance had only been a fleeting glimpse of it and had been more
than six years prior, though the primary motive for recycling the
design was to save money. Robert Bonchune, from Eden FX, agreed with
the reuse, not only owing to the quickness of its previous appearance
but also because it looked extremely different from the ships depicted
before, which was important because the visual uniqueness of the ship
matched how it had been described in the "Babel One" script. (Star
Trek: The Official Starships Collection issue 39, pp. 13 & 14)
The ENT art department created a drawing of the vessel's exterior in a
primarily green Romulan color scheme and with the ship's surface
covered in holographic emitters. After this was approved, the image
was passed on to Robert Bonchune. According to him, the craft was then
given a memorable nickname. "I got a sketch of that ship as a Romulan
ship," Bonchune reflected. "John Eaves [I think] wrote 'FLEA' on it
and that's what it became known as. But officially it was the Romulan
drone and that is it." (Star Trek: The Official Starships Collection
issue 39, pp. 13-14)
After receiving the illustration, Rob Bonchune began modifying the
relevant computer-generated model at Eden FX. "I could have had our
modelers Pierre [Drolet] or Koji [Kuramura] do it," noted Bonchune,
"but that would have just added to what was on their plates." Since
Bonchune himself was already working on the ship's modifications, he
opted to continue doing so. (Star Trek: The Official Starships
Collection issue 39, p. 14)
Because importance was still placed on budget-saving, Rob Bonchune
didn't spend too much time altering the ship's CG model. "I was
changing colors, adding antennas, and rebooting the lights, without
rebuilding it [....] All those things were in place. It was really
just changing colors," he explained. "I illuminated some antennas I
didn't like and changed the internal lighting." The biggest
differences in the CG model took place because, in the six years since
it had originally been built, processing power had greatly increased.
This allowed Bonchune to make the holographic generators on the hull
as elaborate as he wanted. Thus, the model took advantage of the
relatively new ability to turn on ray-tracing lights, which had been
impossible to do for episodes of Star Trek: Voyager due to
insufficient render power. "So I upgraded the lighting," stated
Bonchune. "I put some interactive light in for the holoprojectors and
we could have them glowing, and I made some changes to the point
lights at the end of the bigger antennas. It didn't take long. We gave
them exactly what they wanted – a ship that cost virtually nothing."
(Star Trek: The Official Starships Collection issue 39, p. 14)
Note that this answer is out-of-universe only. These ships aren't intended to be related, and some effort was made to change them slightly so that casual fans wouldn't notice the re-use.
