This thread is for a general all-inclusive discussion of the library card explanation presented by the WTS. Nothing within that context should be considered off-topic.
To get the ball rolling:
By affiliating with the UN as an NGO an organization agrees to support and advance UN goals. To help accomplish this common goal the NGO is issued a grounds pass, is allowed to send representatives to various briefings, meetings and conferences, etc. It also provides the NGO access to policy makers, academics etc.
The whole package is set up so that both the UN and the NGO are aided in promoting whatever subset of goals that they have in common. That is the reason for affiliation - commonly held goals. If an entity only wanted access to the library then it could obtain a library card without affiliating.
For the WTS to claim that they affiliated solely to obtain a library pass is disingenuous in that it ignores the above obligations - essentially a contract between them and the UN. Presumably, they affiliated so that they could meet the terms of their contract with the UN and so, advance their shared goals.
The WTS, and Mr Alward, apparently want to focus on the library or grounds pass as if that were the end in itself. While I personally believe that the WTS screwed up royally and, out of arrogance, affiliated for its own ends, which centered on access to library materials, that is mere speculation on my part. It is also speculation on Alward's part who, for whatever reason, wishes to accept the WTS's explanation uncritically. We must go off the facts which clearly show what the obligations of an NGO are, and what the benefits are that accrue to it - a grounds pass being only one of many.
Focussing on the library card is done only to trivialize the issue so that the WTS doesn't look quite so bad. The fact that the WTS lied in its letter to the Guardian also destroys any reason for giving them the benefit of the doubt.
So in answer to the question "Why did the WTS affiliate?" the only reasonable answer is "to allow them to further the goals and principles they hold in common with the UN." For those are the terms of affiliation. We can speculate all we like, but until the WTS issues a truthful statement that says something like "We screwed up and just did it for the library pass and had no intention of meeting our obligations to support the UN and quit when we found out what was required" or "We just did it for the library pass and were happily meeting our obligations to support the UN until we were found out" then we must accept the terms of affiliation as being the reason they affiliated.
Th etruth is, until the WTS issues a truthful explanation that is consistent with the facts - which might include a statement of being unaware of the UN's policies at the time of their affiliation then we have nothing to go off at all - other than a letter is that is a tissue of lies.