Windows 7 doesn't remove all image EXIF data

Question 1

Why doesn't Windows 7 remove all image EXIF data? The thing is that I don't remember this being an issue in the past. Could it be the case that Window 7 only looks for specific EXIF attributes, ignoring any new attributes that become standardized?

See below pic that illustrates how some attributes are not selectable and, therefore, unremovable.

Question 2

It seems to be a choice of those who designed / wrote the operating system.

You are asking why from the OS interface you cannot directly get rid of those fields... because it is written in this way (see tl;dr).

How to overcome it

If you want to strip (delete) them, you can install, for example, the open source program ImageMagick (search for Windows Binary Release in the download page ^[1]) and then use the command line

magick mogrify -strip  your_filename.jpg

or

mogrify -strip your_filename.jpg

^{The use of magick mogrify or mogrify
depends on the installed version.}

You should be able to select all the files in a directory too (*.jpg, *.*).

Note ^[2]

-strip

strip the image of any profiles, comments or these PNG chunks: bKGD,cHRM,EXIF,gAMA,iCCP,iTXt,sRGB,tEXt,zCCP,zTXt,date.

Exiftools

You can manage each of the EXIF fields with many programs; among the best there are the exiftools ^{[Exiftools Help,Exiftools homepage]}.

ExifTool is a platform-independent Perl library plus a command-line application for reading, writing and editing meta information in a wide variety of files.

P.S. You may want to give it a look to GIMP ^[3], which may allow you to have a simpler way to control (GUI) on the single fields, usually directly accessible when you save as or export as a file.

TL;DR

Exif is a publicly available standard (from 1995). The last releases are exif 2.2 (April 2002), then the current exif 2.31 (issued April 2010 - Revised 2016). If you wish to see the next 2.3x update update will be issued in 2019 and it is already available (with name CIPA DC-X008-Translation-2019).

I reported the tag values for the not selectable fields of your picture here below (related to the current version, taken from exiftools page and checked on the official document).

Mainstream support for windows 7 ended on January 13, 2015. Extended support will end on January 14, 2020.
For example the tag "ExposureTime" is present from the first edition (2002 and it is still unchanged even in the version that has still to born in 2019). So it was present when they develop it and when they released all the updates. So true that you see those fields in that window.

So we have to deduce that...

they decided to do so.

0x829a  ExposureTime           rational64u  ExifIFD
0x9204  ExposureCompensation   rational64s  ExifIFD     (called ExposureBiasValue by the EXIF spec.)
0x920a  FocalLength            rational64u  ExifIFD
0x9205  MaxApertureValue       rational64u  ExifIFD     (displayed as an F number, but stored as an APEX value)
0x9206  SubjectDistance        rational64u  ExifIFD     
0x920b  FlashEnergy