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!