Visual Studio 2017 is still a 32Bit application, Microsoft tried to defend their decision to not provide VS as 64bit in various blog posts.
So by default 32Bit applications install to C:\Program Files (x86)\ and everything is ok what you see.
// Update
The next Visual Studio Version 2022, will be 64Bit to fix the out of memory issues:
The next major release of Visual Studio will be faster, more
approachable, and more lightweight, designed for both learners and
those building industrial scale solutions. For the first time ever,
Visual Studio will be 64-bit.
Visual Studio 2022 will be a 64-bit application, no longer limited to ~4gb of memory in the main devenv.exe process. With a 64-bit Visual Studio on Windows, you can open, edit, run, and debug even the biggest and most complex solutions without running out of memory.