because even Silver Solder is inherently brittle and can tear traces from the board.
Seems that Pb had one set of issues (Toxicity) and now Silver with it's own set (Brittle and Melting point)- well, the days of radio may be numbered because they are so disposable nowadays...
The solder with the highest tensile strength there is, is a silver solder. SN62 / PB36 / AG02. Best solder there is for rework. Super tensile strength and low melting point which is easy on those cheap CB radio circuit boards.