Why aren't there any and are there any planned for the near future?

There are ones currently close enough...east and west within a stones throw, nearly. Personally, I like looking out onto the lake and seeing wide open views with little presence of human invasion. A few sailboats amidst the sunsets are nice...but marinas are essentially parking lots on water, but that's my personal preference.

I think that there are a number marinas that are close to downtown. You can't really get any closer to downtown unless you plan on taking land away from the Port of Cleveland.

i think it would be nice if there was one around here

 

http://maps.google.com/maps?q=41.510827,-81.695044&num=1&t=h&sll=41.510642,-81.695436&sspn=0.002603,0.005617&hl=en&ie=UTF8&ll=41.510831,-81.695114&spn=0.002603,0.005617&z=18

I agree with the "parking lot for boats" sentiment expressed above.  Obviously necessary but not particularly attractive.  Don't see a big clamor for one in the heart of downtown, especially when others are so close.

I noticed that Chicago had several and I thought it would be a nice addition.

Marinas require parking lots.  For downtown, I prefer harbors and docks or slips.  Like what we have at North Coast Harbor and the docks around Shooters... and used to have on the East Bank.  I would expect that FEB will have a dock or a couple slips.