Why make it so that negative slopes are increasing?

[jordantgh]

#' @param x numeric dose vector.
#' @param b steepness
#' @param c lower limit
#' @param d upper limit
#' @param e ED50
meLL.4 <- function(x, b, c, d, e){
  .value <- c + (d-c)/(1 + exp(b*log(x/e)))
  # ...
}

The above is not a conventional way of writing the logistic model that I've seen. Instead I usually see it written as:

fourPL <- function(x, a, b, c, d, e) {
  d + (c - d) / (1 + ((x / e)^b))
}

In the formulation used by this software, curves that exhibit increasing response with respect to dose have negative slope. Is there a reason for this or is it just historical? I understand that changing it now would be a problematic breaking change, but I found it pretty unintuitive.