Physical activity is important also for our mental state. Isolation, voluntary or forced, and social deprivation is very burdensome. Especially when combined with overall fear for our health and job insecurity. Physical activity can be life-saving in this respect as a wave of suicides is already sweeping the world, often committed by people with no known history of disorders. In simple words, it's easy to plummet into darkness very quickly even if you don't contract the virus yourself. Staying fit will help you avoid a crisis of your own.
Even if you're locked at home, you should find plenty of opportunities to remain active. As fitness clubs have closed their on-site facilities, they're switching online and streaming training programmes for individuals and groups. Many of them are free and if they're not, please consider helping out these coaches, many of them have lost their regular income already.
On a final note, remember that you don't only have to be fit. Proper nutrition, hydration and getting enough sleep will also prove very helpful if you happen to contract the coronavirus. If possible, avoid or limit smoking and alcohol – they may be seen as a stress relief, but they're weakening your body.