If your bike is good and you can really go all-out, no problem. Thing is, most people are limited by using a standard treadmill and think they did something close to 100%. If simply effort would translate that easily into the corresponding stimulus, all we’d need is pushups and burpees.
True sprints on track allow your body to not only become fast but demand to be able to switch rapidly between relaxation and force production while coordinating all of the body’s muscles for what it’s fundamentally built. This is very difficult to replicate with machines as you essentially load the switch phase of your stride needlessly with weights. Personally, I had no luck so far and the track always worked far better for me than any machine I got my hands on.
(To be fair, anything over 3,4 sprints @95+% is very taxing and might very well reduce your numbers the next day. So a decent AssBike might perhaps allow you to reap the benefits while not stressing the body too much at the same time, who knows.)