You can sort of see why they used it; it's a fairly common metal. It's really easy to work. You can use it in paints, glazes, or cast objects from it. It doesn't rust or otherwise deteriorate. there's really only one significant problem with it;
If you ingest it, it's a poison.
In fact, some historians have suggested that as such it may have played a role in the problems in the later Roman period:
"S. Columba Gilfillan proposed a theory for Roman decay in 1965 that involved "poisons esteemed as delicious by the ancient well-to-do." Spoilage was a problem in ancient Rome, and vintners discovered that wine tasted better and lasted longer if it was mixed with a concentrated grape syrup called sapa. The best sapa was boiled in lead pots, allowing lead to leach into the syrup. When sapa was mixed with wine, it sweetened it and also poisoned the microorganisms that cause fermentation and souring. Sapa was also used in fruit and honey drinks, and as a food preservative.It's difficult to say whether all this lead was a genuine problem; there were enough other problems to make things interesting long before the lead got in there - untreatable epidemic disease, widespread poverty and slavery, poor hygiene, bad diet.
Josef Eisinger estimated a Roman consuming a liter of wine a day would ingest about 20 mg of lead per day, which he said was more than enough to produce chronic lead poisoning.
A cultural shift at the height of the Roman Empire made it socially acceptable for wives to drink wine, to which Gilfillan attributed a declining birth rate and a low rate of surviving children among the wealthy. Today, the reproductive effects of lead are well established, as are the effects on childhood development and learning disabilities.
Gilfillan hypothesized that the diet of the poor was not so badly poisoned as that of the rich. Although they drank the same water, they lacked the luxuries of cosmetics, lead paint, wine, fruit and honey drinks, or preserved foods."
But, still...interesting tidbit of history.