I’m not sure what prompted potters to make plates especially to serve bread on…

But a clue is possibly in a line from The Lords Prayer...

"Give us this day our daily bread”

which is reproduced on the rim of so many examples of Bread Plates..

F & R Pratt (1865)

 (Unknown Potter)

WASTE NOT WANT NOT…

(Copeland)

Initiated by Pugin and Minton and copied by numerous other potters, (this example is by Copeland) "Waste not Want not" was a constant proverb for the poor in Victorian times, suggesting these plates were made primarily for the working classes. 

So maybe the plates were a way of reinforcing Victorian values at every day mealtimes...