Why on a line graph do all the points not fit exactly on the line?

because they are annoying like that.

the reason it's called a line graph is because you join up the dots with a line.

or you can leave the dots unjoined (a scatter graph) and draw a line of best fit.

this is a line that doesn't touch any of the dots, but has a roughly equal amount on each side. there is no right or wrong line of best fit, but you cant have, say, 4 dots on one side and 1 on the other. the point of 'lines of best fit' are to show roughly where the dots go - the pattern of the data.

HOWEVER, if drawing a line of best fit, you must first identify, then discredit any ANOMALIES, which are results of the data that are very different to the other answers; they do not fit into the pattern.