ggpairs factor not labeling as expected

I have the following data, and I transform "method" to a factor then do a ggpairs plot. However, as you can see, the ggpairs plot does not label the two factor levels in the output as I expected. based on other examples, it should label "MBI" and "traditional" above the box-plots.

structure(list(ID = c(4L, 5L, 6L, 8L, 12L, 13L, 15L, 16L, 17L, 18L, 21L, 22L, 24L, 25L, 28L, 29L, 30L, 31L, 33L, 34L, 35L, 36L, 37L, 39L, 40L, 44L, 46L, 48L, 49L, 51L, 52L, 53L, 54L, 55L, 56L, 57L, 60L), OptPost = c(50L, 67L, 61L, 92L, 59L, 16L, 42L, 69L, 42L, 59L, 44L, 52L, 84L, 91L, 84L, 59L, 84L, 84L, 59L, 67L, 67L, 67L, 70L, 50L, 84L, 50L, 20L, 46L, 42L, 44L, 46L, 50L, 55L, 75L, 50L, 39L, 55L), method = c("MBI", "MBI", "MBI", "MBI", "MBI", "MBI", "MBI", "MBI", "MBI", "MBI", "MBI", "MBI", "MBI", "MBI", "MBI", "MBI", "MBI", "MBI", "MBI", "MBI", "MBI", "traditional", "traditional", "traditional", "traditional", "traditional", "traditional", "traditional", "traditional", "traditional", "traditional", "traditional", "traditional", "traditional", "traditional", "traditional", "traditional"), gender = c(0L, 0L, 0L, 0L, 1L, 1L, 0L, 1L, 1L, 1L, 0L, 1L, 0L, 0L, 0L, 0L, 0L, 1L, 0L, 0L, 1L, 1L, 1L, 0L, 0L, 1L, 0L, 0L, 1L, 0L, 1L, 0L, 0L, 1L, 0L, 0L, 1L), OptPre = c(50L, 50L, 30L, 67L, 42L, 8L, 8L, 12L, 42L, 50L, 0L, 25L, 50L, 83L, 17L, 17L, 24L, 44L, 44L, 44L, 28L, 55L, 58L, 42L, 71L, 41L, 15L, 42L, 17L, 44L, 16L, 32L, 50L, 42L, 32L, 30L, 42L)), class = "data.frame", row.names = c(NA, -37L))optics_df <- optics_df %>% mutate(method = as.factor(method))ggpairs(optics_df[, -1],        mapping = ggplot2::aes(color = method),)ggpairs(optics_df[, -1], aes(color = method)) #same as above

I attempted to ggpairs plot for a dataset, expected factor to be labeled automatically yet it is not.

Note: while a legend is acceptable as a solution, we really want it to be included in the labels as with this example for gender:ggpairs plot example

edit:the answers provided so far are good and very helpful! but they don't fix the issue of labeling the actual column, they only add a legend.

I did some additional experimenting and I was able to notice that when we move the 'method' column to the end of the dataframe, the labels are generated automatically. can someone with a better understanding of ggpairs explain why this is the case?