It’s also possible that we catch those but our immune systems fight them off and we don’t notice.

However:

COVID19 is 30x more deadly and almost 2x more contagious than the flu. We have no existing immunity to COVID19.

https://twitter.com/VirusesImmunity/status/1238475009712160769

This article looks really good with some good info too:

One of the few mercies during this crisis is that, by their nature, individual coronaviruses are easily destroyed. Each virus particle consists of a small set of genes, enclosed by a sphere of fatty lipid molecules, and because lipid shells are easily torn apart by soap, 20 seconds of thorough hand-washing can take one down. Lipid shells are also vulnerable to the elements; a recent study shows that the new coronavirus, SARS-CoV-2, survives for no more than a day on cardboard, and about two to three days on steel and plastic. These viruses don’t endure in the world. They need bodies.

To be clear, SARS-CoV-2 is not the flu. It causes a disease with different symptoms, spreads and kills more readily, and belongs to a completely different family of viruses. This family, the coronaviruses, includes just six other members that infect humans. Four of them—OC43, HKU1, NL63, and 229E—have been gently annoying humans for more than a century, causing a third of common colds. The other two—MERS and SARS (or “SARS-classic,” as some virologists have started calling it)—both cause far more severe disease. Why was this seventh coronavirus the one to go pandemic?

…but I wonder why does it appear to be more contagious than other viruses such as colds and flus? Assuming it behaves like other Coronaviruses.

I’ve probably had a flu once or twice in the last 10 years and a cold a handful of times (even when people nearby have had it).

Are we likely to see a dormant-like state of it? Like with HSV - which only results in symptoms when you are run down, etc? Maybe it will reach the infection rates of other viruses such as HPV. Perhaps people will carry it from a young age, but it will only create issues as they get older…

Flu is not a coronavirus, while common Cold virus are.
This is a novel virus for humanity, only recently it made the species jump from presumably bats to humans. No one has ever encountered it yet, there is no herd immunity against it reducing its spread from person to person. It is airborne transmisible, and asymptomatic or presymptomatics can infect a large number of people without even knowing they are infected. All this can account for its high rate of contagious.