The reason the vaccine was withdrawn from offer to the general population under a specified age (which varies by country) is because of concern over the risk / reward ratio.
Unfortunately no drug is risk free, take paracetamol, about 0.6% of the population would suffer an allergic reaction of note to paracetamol, a much smaller percentage would have a fatal reaction - If i gave everyone in the world a paracetamol it would result in at least thousands of deaths, and even more allergy consequences.
Vaccines too can have serious side effects, some of the ones used for tropical diseases are really rather nasty. The Covid vaccine does have side effects that are known (heart symptoms) and other possibles (recurrence of cancer for example), the possibles based on small reporting may come to nothing. Then there is long term effects, which won't be known for 10-20 years.
The regulators have deemed, very sensibly in my opinion, that for those not at great risk from the virus you are better off, having had a course of vaccine, and likely been infected too, that your hybrid immunity should keep you safe, and the risk of the vaccine is equal to or greater than the risk of the virus, hence no benefit.
Speaking as a science teacher, I think the development of the mRNA technology employed in the vaccine is a truly amazing bit of science, and done very efficiently in time of crisis, it will certainly serve humanity well in the future - but as a 44 year old, thrice vaccinated, and infected, I think the vaccine is best used for vulnerable groups until we know far more about its risks, and understand the mechanism behind long covid - science will get there.
As to Dr John Campbell, as an educator I find him an enjoyable and able analyst and presenter of information - he doesn't shy away from looking at the good, the bad and the ugly of the covid phenomenon explaining clearly theories and data as they land. He has a Phd so is quite within his rights to be called Dr. and is well regarded as an author of medical textbooks used in nursing training, I would say he has an open mind, which is good, in science, especially actively developing science you really need that. (as a side fact most UK medical doctors hold no doctorate but rather a double bachelors degree)