Closing as by design, it's deliberately not included. It's very hard to accurately estimate the final download size at export, because the export process involves sophisticated script minification processes (using Google Closure Compiler), and much more significantly, sophisticated image spritesheeting and recompression. This can change the size of the project by megabytes, so the estimated size is deliberately very rough. If it could be accurate to within 1mb that would be an excellent result, and usually the total script size is under 1mb, so for the purposes of the estimation the script size is basically negligable.