converting igbb classification to factor?

I'm wondering why the round function needs to be applied to the IGBP classification- why isn't it already a round number? 

# Converting the raster object into a dataframe and converting the IGBP classification into a factor
IGBP_df <- as.data.frame(IGBP_raster, xy = TRUE, na.rm = TRUE) %>%
  mutate(MCD12Q1_LC1_2019_001 = as.factor(round(MCD12Q1_LC1_2019_001)))