Seasonal flu has been around for so long that there are readily available average year figures that governments and health services can use to prepare, so that they know they will need an average of x number of beds in that season, and x amount of oxygen available for that season. Some seasons have higher than average numbers of cases and hospitals in some places do struggle.
With the flu vaccine, and so many higher risk groups having good uptake of the vaccine, and now also pneumonia vaccines, many hospitals have fewer beds than they used to need for an average flu season.
We don't yet know what the peak number will be for Covid-19, but even if it's the same as for the average flu season...if it were to coincide with the peak of flu season, then you'd need twice as many hospital beds, oxygen, ecmo units as normal....and in most places that isn't doable.
This isn't instead of the flu season, this is on top of it.
In the UK, non-emergency operations are often delayed during flu season, then they try to catch up when they get over flu season. This year, instead of being able to catch up outside flu season, they're going to be very concerned about having ICU beds open for Covid-19 pneumonia patients, so instead of using the summer to catch up on non-emergency operations, they might have to put off those operations again in order to treat Covid-19 patients.
And if the peak number of Covid-19 patients is higher than the average flu peak....they won't be able to cope, because they can barely cope now at peak of flu season. That's what Italy is seeing now.
Of course, there is a little bit of a heads up for us with Covid-19, unlike for Hubei. And we will have a few more weeks than Italy had to prepare. So our government is planning to bring healthcare staff out of retirement, or those who've left their healthcare jobs for other careers, they're going to be asked to come back to working in the hospitals for the duration of the outbreak, in the hope that that will help them have enough staff to care for the patients....and unlike flu, the doctors and nurses haven't had vaccinations for Covid-19, and they're going to be treating Covid-19 patients, including those who come in for other reasons, not diagnosed before they come in....and if an undiagnosed case comes in for an appendectomy, then the nursing staff won't be wearing the full hazmat-type protective suits and are at risk of coming down with Covid-19. Whereas if that patient had flu, the staff would have been vaccinated and it wouldn't be as much of a problem.
Hubei was able to bring in doctors and nurses from outside Hubei to help them cope with all the extra patients. I presume they also brought in other items like oxygen and ecmo from outside Hubei. If it takes off in another country in all the counties/provinces/states/major cities at one time....there's no less-affected 'outside' to bring those staff and items from.