Being healthy is not a certain indicator that the illness is going to be mild for you. It will most likely be light, but there's no guarantee about this being true.
And even if you don't end up in the ICU, you still risk complications which may hamper your health long term (see "long Covid"), or that could cause you long-term issues like an hampered sense of taste and smell. This is mostly avoidable by getting inoculated with one of the vaccines, which while they might not reduce to zero your chances of getting sick, they will basically zero any chance you have of serious complications. It's also very likely vaccinated people are less infectious after a jab.
All of this comes at the cost of a really small potential risk of side effects, each of one ostensibly much less likely than the chance of getting seriously sick due to the virus itself.
About the flu: we don't need to vaccinate everyone every year because usually people get one strain of the flu or another during their lives. Sars-CoV-II, on the other hand, is a completely new virus. See for instance what happened when during the Columbian exchange, where Rhinoviruses were introduced by the Europeans in the Americas. The natives had no kind of immunity for the common cold, so millions of people got seriously sick and died from an infection that did basically nothing to the Europeans.
Also, I must say it's morally reprehensible to not getting vaccinated during a pandemic, unless you plan staying isolated until the emergency ends (i.e even if and when the vaccinated will go out, you should still stay home). While you might not _need_ the jab, you could still spread the virus and help the infection reach new hosts. Vaccines are never 100% effective, some people with compromised immune systems do not develop strong antibodies, and that's why it is crucial to vaccinate everyone, both healthy and vulnerable.