Why are single celled organisms so small?

Answer 1

Think about this as in you were living in a small apartment or a large mansion. If you had to run to the kitchen to grab a snack, which location would be easier to do this in?

Another way to think about this is what reason, or pressure, would they organisms have to get larger? Bacteria don't have organelles the same way eukaryotic (ex. plant/animal cells) do so they don't need lots of room.