There are so many ways your bicycle can be reused and you may even collect some money for your old one and help pay for the new one. There are NFPs in most capital cities who collect old bikes, but here are a few options to re-home or re-purpose your bicycle:
For the past one hundred years or so, bicycle frames have been mostly made from steel tubing. Over the years, the walls of the tubing has thinned out and bikes become lighter. Steel is still used, but bike frames are now also made of titanium, aluminium and increasingly of carbon fibre, especially as it becomes cheaper to make.
Carbon fibre is an environmental nightmare. The carbon fibre production process is dirty, it is difficult to repair, expensive to recycle and it isn't particularly biodegradable. Carbon fibre is a composite product, designed to last for a very long time and that is just what it is doing in landfill.