git versus CVS (versus bk)

My memory is playing tricks on me.  I seem to remember running linux
in the 1980's, but the earliest kernel I can find on kernel.org is
dated 1994.  Maybe I'm remembering xenix...dunno.

Anyway, I've been tracking Linus's kernel for many years -- long
before bitkeeper or git.

I know just enough to compile and run a kernel, but not enough to
be a software developer.  And that is where my question comes from:

Could someone explain to me the shortcomings of CVS which prompted
the development of bk (and then git) -- in a way that a non-developer
like me can understand?  Pretend that you are Albert Einstein, trying
to explain your theories to a ten-year-old -- this is always a useful
exercise for those of you who are drowning in micro-details!

I've already done some googling on this subject, but everything I've
found is drenched in those micro-details which make the subject
opaque to me.

Thanks for any pointers!