I will use results for two age groups in one marathon to ask the question.
In the 2019 New York Marathon. 1,945 people age 30 to 34 took more than 5 Hours to finish.
With their poor performance at such a young age, should those people be running marathons ?
356 people age 25 to 29 took more than 6 Hours.
I am almost 60 and I could walk a marathon in 12 Hours, but that would be absurd.
I understand your question, but with an enormous charity component in the marathon, we don't know who these people are and what they represent. Not everyone is taking part to place in their age group or run a PB. It is a great privilege to be in a sport that makes such a difference in lives in such a variety of ways. I hope it continues to make a positive difference in your life!