From what I can gather there are a number of reasons.
Firstly, the industry, rightly so, has far more red tape than it used to. I know of my great grandparents chartering a number of aircraft 40-odd years ago to take them, family, friends and others to the other side of the pond and they did so from their living room. Not for profit, simply as a means for all to get across to the other side. They were also far from well off. It is now pretty illegal for me now to ring up say Astraeus, ask for one of their 757s to take me along with a hundred others I could sell tickets to to YYZ in August. Even if I didn't make a penny profit.
Secondly, as you say, links get lost. Family members die and ties deteriorate sadly.
Finally, and what I believe is most important. It's just as cheap, maybe cheaper, to book on the dozens of other options available to all to get to Canada from the UK. AC, LH, BA, VS, AF, KL, US, AA, UA/CO, DL etc etc can all take me there anytime of the year for a reasonable fare both at the front and back of cabin.
As you say, times change.