Because it's a virus?

Well, It...

Uses more and more system resources.

Takes up more and more hard drive space.

Writes files all over your system in places you never will find them all.

Deletes files from your system without you knowing.

Randomly crashes your system.

Randomly locks your system.

Randomly trashes your hard drive.

Actually Windows 95 can't be a virus because;

Viruses are free...

Viruses don't take up most of your hard drive...

Viruses don't need 80 megs of RAM...

Viruses don't have major bugs...

Viruses don't have three different sets of documentation...

Viruses don't leak info to the press about the upcomming Jerusalem 95, to keep people from switching to Michelangelo/2 Warp...

Nobody cares if a virus turns out to be 16 bit, even though it is advertised as 32...

Viruses self replicate...

Viruses install themselves !