Cavendish, focault and schihallion experiments all used lead. Hmm mm. Strange that. Why not use a non conductor? All use lead?
Because the gravitational force is proportion to the masses and inversely proportional to the square of the distances, to make the forces large enough to measure with a reasonably small experimental rig - you need BIG masses and SMALL distances - which means you need a very dense material.
There are certainly denser materials than Lead - if we list all of the elements in order of densest to least dense, the first nine elements have to be made synthetically because they don't exist in nature. If we exclude elements that are so crazily rare that you can't get enough to do an experiment with, then you end up with the list:
Iridium, Platinum, Plutonium, Gold, Tungsten, Uranium, Tantalum, Mercury, Palladium, Thallium, Thorium...and Lead
If we remove the toxic and horribly radioactive ones, we end up with:
Osmium, Iridium, Platinum, Gold, Tungsten, Tantalum, Palladium, Thallium, Thorium...and Lead
Of these, some are VERY expensive - and to make masses that are large enough to produce a measurable force - we need LOTS of material.
So when we trim it down to the cheapest/densest material available - we're pretty much left with Lead.
Even if you were to persuade someone to lend you a couple of tons of gold or tungsten to meld down to do the experiment - these are all metals.
The densest NON-metal is Iodine - but it's density is less than half that of Lead...and it's still pretty expensive in a concentrated form...the next non conductor is Bromine...same problem...Carbon is the next densest non-metal - but that's also a conductor, then Sulphur...but that's less than one fifth of the density of Lead.
So no great mystery - they used lead because it's really the only substance that's dense enough, safe enough and cheap enough in large quantities.
Mercury would perhaps have been a good second choice - but the experiment involves the masses moving around and mercury (being a liquid) would tend to slosh around. But it's also toxic and pretty expensive.