This is quite idiomatic for R; packages like ggplot do the same thing to, for instance, build up graphics- see https://r4ds.hadley.nz/data-visualize for some nice examples
ggplot2 is pretty much an exception at this point, and if the package was created today it would use the pipe instead of add [1]. Most packages use pipes now (especially with the introduction of the pipe operator in R 4.1.0).
I am no R expert, but pipes don't seem the most intuitive for ggplot. This is because they would imply that, e.g., ggtitle() %>% geom_point() means that ggtitle() outputs an input for geom_point().
