Hybrid bikes from 20 odd years ago came in many flavors, some with dreaded front suspension or super upright riding positions but there were also many "sporty" ones whose geometry more resembled road bikes albeit with longer top tubes.
By now, there are a ton of these bikes on the second hand market and they are largely forgotten and cheap, particularly if they need some work to get going again and as they are now old, many sellers are unaware of the quality level of the various models so bargains abound. And some of these had decent components like Deore XT or Ultegra gearing, CrMo or decent Aluminium frames, Carbon forks and threadless stems etc.
It would seem these would make ideal bikes to make a budget drop-bar conversion gravel bike. Throw on a pair of drop bars, some old shifters or cheap Chinese ones, perhaps change the brakes to mini V brakes, new tires (most will take 40mm tires) and you've got gravel on a budget. A search of this shows some people have done the conversions but it seems there is way more interest in converting old MTB bikes to 700c wheels or even old 27" to 700 conversion.
Below are some of the models I think would work.
Felt SR 51, 71 or high end 81
Giant CRX series. CRX 4 is low end and CRX1 high end.
Jamis Coda series. Sport or high end Comp.
Trek 7700 series.

So why not?