To advice someone who has 40 years of experience as someone who has zero experience does sound "a bit" unadequate to me... Just because you don't get it this does not mean that everyone apart from you is mad... As far as I understand it you currently have neither experience with folding bikes nor with trailers nor with recumbents or trikes. And it seems as well not so much with generic patterns of what's important if you ride a bike intensively. Not so sure if that is really a good starting point to advice and judge on others... Your not understanding may simply be the result of your level of know how, not of a higher level of cleverness. I.e.: If you ever would have traveled with public transport and bike combined away from the most major routes you would easily understand why one might use a Brompton for that. If you ever travelled with a Brompton you would easily understand why people use the front luggage option on it and clearly why they prefer it over a trailer in most cases - you probably would understand that part if you had experience in travelling with a trailer. Stop judging, start learning.