Exactly this.

It’s macabre, but its high mortality rate and small window of transmissibility before symptoms appear, pretty much keeps this from becoming a pandemic. It’s too effective at killing the host.

Something like COVID survives because it has a mortality rate a hundredth of this, but has a huge window of transmissibility before symptoms start appearing, or the symptoms are very mild.

The larger that window, the scarier a virus gets.

Hentavirus is terrifying if you do contract it, because you’ve got roughly a 1 in 3 chance of dying, but that mortality rate is also the reason why it’s not going to spread to every corner of the world.