Hardware drivers...
Windows 7 is no longer supported for newer hardware...

On top of that, a lot of software no longer gets updates for windows 7, so you are forced to use older versions..


Let me ask you another question, is there a reason not to upgrade to windows 10, espescially since it was once a free update?
I will answer this, only on older pc hardware, where there where never windows 10 drivers released..
But i. That case, you ought to buy new hardware anyway, as its obsolete...