A regular topic that comes up on genealogy forums is the lack of documentation of sources especially on large trees.
I believe there are a number of reasons why the larger online trees do not have sources.
Many people start trees online then give up once they get to grandparents or beyond the people they remember and these trees are often unsourced as they have been produced as a passing whim. There are a large number of these on websites such as Genes Reunited which are free or minimal cost. When they go back to these later they do not think that they have not added information as to where they found out how these people fit in their family.
Very few of us can say we documented all our sources from the start and we can be reluctant to go back and add them later, even though it may save us time overall.
Few of us trust everything we read and given the rate information is added to the internet we do not always want others to use the information we have obtained at our own expense.
Basically the reasons for not including sources in online trees as I see it are :
- Lack of trust of others
- Cost associated with obtaining the information
Don't criticise others who seem to be unwilling to share but do as you would like to be done by.
If you choose not to put your sources on your tree mention this in the opening page.
If you are willing to share with others invite them to contact you.
Some of my best leads have come from others but by confirming things for myself I have found information beyond what others have given me which has made this hobby so much more enjoyable.
Those who just include other peoples research do not know the joy of discovering something new for themselves.