To start off, GIMP is hardly an analog of photoshop. Being the best open source product, does not mean you're comparable to the proprietary 600 lb gorilla.
I recently learned that GIMP is a Photoshop replacement in Ubuntu world and Photoshop that I knew was a huge application around 500MB
That's not even close to the size of GIMP. For example the GIMP packaged depends on the following,
Depends: libgimp2.0 (>= 2.10.6), libgimp2.0 (<= 2.10.6-z), gimp-data (>= 2.10.6), gimp-data (<= 2.10.6-z), libgdk-pixbuf2.0-0 (>= 2.27.1), xdg-utils, libaa1 (>= 1.4p5), libbabl-0.1-0 (>= 0.1.10), libbz2-1.0, libc6 (>= 2.27), libcairo2 (>= 1.12.2), libfontconfig1 (>= 2.12.6), libfreetype6 (>= 2.2.1), libgcc1 (>= 1:3.0), libgegl-0.4-0 (>= 0.4.8), libgexiv2-2 (>= 0.10.6), libglib2.0-0 (>= 2.55.2), libgs9 (>= 8.61.dfsg.1), libgtk2.0-0 (>= 2.24.10), libgudev-1.0-0 (>= 167), libharfbuzz0b (>= 0.6.0), libheif1 (>= 1.1.0), libilmbase23 (>= 2.2.0), libjpeg8 (>= 8c), liblcms2-2 (>= 2.8), liblzma5 (>= 5.1.1alpha+20120614), libmng2 (>= 1.0.10), libmypaint-1.3-0 (>= 1.3.0), libopenexr23, libopenjp2-7 (>= 2.0.0), libpango-1.0-0 (>= 1.29.4), libpangocairo-1.0-0 (>= 1.29.4), libpangoft2-1.0-0 (>= 1.29.4), libpng16-16 (>= 1.6.2-1), libpoppler-glib8 (>= 0.44.0), librsvg2-2 (>= 2.14.4), libstdc++6 (>= 5.2), libtiff5 (>= 4.0.3), libwebp6 (>= 0.5.1), libwebpdemux2 (>= 0.5.1), libwebpmux3 (>= 0.6.1-2), libwmf0.2-7 (>= 0.2.8.4), libx11-6, libxcursor1 (>> 1.1.2), libxext6, libxfixes3, libxmu6, libxpm4, zlib1g (>= 1:1.1.4)
Because Ubuntu is not a rolling distro, it's safe for the build of GIMP to assume that those versions are present on the system, when you go to install. However, Windows and like operating systems do not provide a repository to satisfy those dependencies; therefore, they can not make such bold assumptions. This means that the above libraries must be statically linked in, or they must be provided themselves.
Moreover, while all the libraries of above must be packaged by Photoshop on Windows, Adobe must further cover other issues,
Microsoft Windows 7 with Service Pack 1 (64-bit)*, Windows 10** (Version 1709 or later)
They have one download for 2 versions of Windows.