From Reddit with all sources included:

see this post https://www.reddit.com/r/Coronavirus/comments/f8k2nj/why_sarscov2_is_not_just_the_flu_with_sources/

The virulence (R0) of SARS-CoV-2 is estimated between 1.4-6.49, with a mean estimate of 3.28[1] . This mean estimate is much higher than the seasonal flu, which has an R0 of 1.3[2] . What this means is that SARS-CoV-2 spreads signficantly faster than the seasonal flu.

The Case Fatality Rate (CFR) of SARS-CoV-2 is at least 2-3%[3] . This is 20-30 times higher than the CFR of the season flu, which is around .1%[4] .

SARS-CoV-2 can be transmitted without the infected showing any symptoms[5] . This makes it much more difficult to control.

Roughly 20% of SARS-CoV-2 infections result in serious symptoms that require medical intervention[6] . This is more than 10 times the hospitalization rate of the seasonal flu[7].

Symptoms from SARS-CoV-2 can persist over a month[8] compared to the seasonal flu where symptoms typically tend to clear after 5 days[9] .

There is no vaccine for SARS-CoV-2[10] whereas people regularly get annual flu shots.

There is no herd immunity for SARS-CoV-2 which means that it can theoretically infect the entire population. See, for example, a Korean psychiatric department where the virus infected 99/102 people.

Now, consider the multiplicative effect that all of these attributes have for the virus. Compared to the seasonal flu, SARS-CoV-2 (1) spreads faster; (2) kills far more; (3) is harder to control; (4) requires use of far more medical resources; (5) for far longer a period of time; (6) has no effective treatment; and (7) can infect entire populations.

These factors mean that SARS-CoV-2, if left unchecked, is far more likely to overwhelm a country's medical infrastructure. Additionally, when medical infrastructure is overwhelmed, the CFR will skyrocket because we know that 20% of cases require medical intervention.

It doesn't take a genius to piece it all together. This virus is potentially devastating if containment measures fail. Far worse than the seasonal flu.