Why is it not practical for insoluble salts to be prepared from other insoluble salts? My textbook says that it is not practically feasible to make insoluble salts (say PbSO4) from other insoluble salts (say PbO), without explicitly mentioning the reason for the same.

My guess is: if the product is also an insoluble salt, it may deposit on the insoluble reactant, and stop further reaction. However, isn't this problem solved by simply stirring? (Is the constant stirring required the reason why such a method would not be "practically feasible"? But isn't stirring rather common for chemical reactions?)

So, what is the actual reason?
The comment "My textbook says that it is not practically feasible to make insoluble salts (say PbSO4) from other insoluble salts" is not precisely accurate. Limited solubility in water does not necessarily imply a lack of solubility in an acidic medium. 

For example, I have prepared Silver acetate (moderately water-soluble, see Table) from the action of dilute acetic acid and 3% H2O2 in the presence of an electrolyte (a small amount of KNO3). Jumpstart the reaction in a microwave. The created Silver acetate is somewhat soluble in acetic acid (see this), hence there is no issue in the creation reaction.

The addition of moderately soluble PbCl2 to Silver acetate/acetic acid likely creates insoluble AgCl and Lead acetate (where the Silver acetate is also moderately water-soluble with respect to water). An explanation of solubility properties, per reference above, relates to a possible creation of an acetic acid salt.