It is you who fails to grasp.
Had the whole world implemented temporary pandemic border restrictions (the only country in the world with completely closed borders is North Korea) the whole thing would have been over with in a few short months.
Temporary border restrictions, and isolating the small number of cases already around, and the misery of the last 2 years would be just a bad dream.
SARS-Cov-2 would never have had the chance to spread so widely, wreak so much health and economic damage, and mutate.
South Korea, Singapore, Japan, Hong Kong, Taiwan, NZ, Australia, Vietnam, and yes China too.
All continued genuinely essential travel in and out. Freight, emergency, etc.
Compare our death rates, and separately sheer number of deaths and long term disabilities, with theirs.
And guess which economies suffered worse. Hint, not Asia Pacific.
Our cure? Repeated lockdowns, mass death and disability, ruined businesses, mental health tsunami, huge NHS backlog (and dead and long term sick HCP). Nearly two years of misery and long-term domestic restrictions.
Yeah. Temporary border control was always the better way. For lives, health and the economy.
It's too late now (save for a miraculous worldwide agreement to do a couple of months) but it's vitally important to acknowledge and remember the mistakes of history. Lessons need to be learned.... For the next time.