but with the added attraction that there were no effective copyright laws in those times.

Actually there were but the situation was in a state of flux. The first British copyright act in the modern sense was enacted in 1709 as a replacement for the monopoly on publishing held by the Stationers Company in London which the government had allowed to expire in 1698. This did not suit the London publishers as they lost their monopoly and they fought to defend it. The situation was eventually resolved in a House of Lords ruling in 1774.

Walsh, being a London publisher would very likely have been among those seeking to defend the monopoly "rights" of the London publishers