The bridge itself has a small path to walk on but not a very high wall over the river making it feel unsafe on a bike. The path is also not particularly wide, especially compared to the car lanes. At the end of the bridge you can get down to the waterfront area but you still need to cross quite a few blocks of parking lots and roads before actually getting to the GAP.

I'm not saying it's impossible, just very uncomfortable to do on a bike. In general, people will get to places in ways that are comfortable and feel safe to them, and the current layout of the bridge does not really encourage doing that without a car. If we want to be serious about getting people to go places without cars, it needs to be comfortable and easy to do so for more people