As far as I know, the border between Morocco and Algeria is still closed, and has been for years. If you start in Tunisia, then it is doable to go east to Egypt and then south to Kenya - a not so uncommon route, though not very popular. Then again, with recent events in this entire region, especially in Libya and Egypt, I am not so sure how safe or volatile the situation is right now.
There is a route depicted in Adventure motorcycling handbook by a map only that takes you from Dakar, Senegal, through Mali, Niger, Nigeria, Chad, and Sudan. If you made your way down to Senagal, then East to Sudan, and then you could easily go South to Kenya... I am myself researching this route, and have found very little information about it. All I seem to find is "..stay the hell out of Chad, and if you are there, get the hell out..." type of info. Chad has plenty of all the most extreme dangers that Africa has to offer it seems, I'm letting this rest for now.
It seems that the only viable option, if you have to start in Morocco, and if you have to finish in Kenya, and if you have to ride the whole way, is to make it down western Africa all the way south, then east a bit, then north again - pretty much going arround most of all of africa, for example: Morocco, Western Sahara, Mauritania, Senegal, Mali, Burkina Faso Niger, Nigeria, Cameroon, Equitorial Guinea, Congo, Democaratic republic of Congo, Angola.... and then unless you feel it safer and easier to go even further south, go east to Zambia, then North to Tanzania and finally Kenya. As far as I know, after getting to Mali, things will gradually get more risky and challenging, and not turn for the better until you get closer to exiting Angola. Having gotten this far though you might as well get South Africa and Botswana in your itinerary. I have personally not been through all of these countries, so it might pay to get second opinions. Going up the east side is easy though, as is most of the way from Morocco to Senegal.
Other common options is to fly into South Africa and ride: South Africa, Botswana, Zambia, Tanzania, Kenya (very easy route). Another common route is from the North East: Egypt, Ethiopia, Sudan, Kenya. There are several ports in Europe that can take you to Egypt. If you insist on riding all the way from Europe, then Turkey, Syria (not sure how safe this is right now), Jordan (safe right now), then Egypt. If you go through Israel you will need two passports, one just for Israel, as some countries may not let you in if you have an Israeli stamp in your passport.
In short, there is no easy route from Morocco to Kenya. Please prove me wrong, then I'll go with you