That's as it should be. Even on a clean install (as I did) it's what Windows uses. There is no system64, but there is a sysWOW64. Same for Windows 7 and Windows 10.
For the why, you have to ask Microsofts Windows design team.

Why does your system still show you're running Win7 Pro 64 bit, if you upgraded to Win10 Pro? That's strange. Or a typo?