Why Buy Rolls?

It's not clear if you are asking about cents, nickels, silver or something else.

Some rolls are bought and sold as BUs, like many modern cent rolls and same late date wheat rolls. Some rolls are sold as "unsearched" circulated wheat, Indian cent or Buffalo nickel rolls for the fun of searching (and hoping to find something decent, which doesn't happen much).

So, maybe some BU rolls for long-term investment, some mixed circulated rolls for searching, circulated rolls from the bank for searching, and silver rolls for investing would be my guess.

I'm building a modern Lincoln BU set. Lots of collectors collect rolls sets. I also like buying them to bust them open and cherry pick.

Many people do as an investment. I've seen many people buy rolls at coin shows of all denominations for possible future growth potential. One person I know has to buy a few rolls for a friend of his at every show he goes to. And of any denomimation. The way some think of it is imagine if you purchased a roll of 1909S VDB cents in 1909, kept them to today. Or you purchased a roll of 1955 cents and they were all doubled. Or a roll of 2000 Roosevelt dimes opened in the year 3000. Last one possible but silly of course.
I suspect too that there are people out there with to much room in their houses and they just want to fill them with something.