All imho, but :
First, because the club thinks, under the rules, they aren't required to.
Second, because if the club started giving information they aren't required to, the PL could have asked for more and more and a refusal to do so, having done it once, could be seen negatively. It's a question of controlling the information flow.
Put it this way, at CAS the club provided an analysis of payments made by ADUG over a certain threshold to show that no monies had gone from ADUG to Etihad. UEFA had some concerns about this report. Had the club presented this report to the CFCB, UEFA could have asked for changes to the report, different information. At CAS, the tribunal could only balance the relevant of weight of the report presented and UEFA's concerns on it. There were no negative connotations to be drawn from the procedure.
Always a rule. Never volunteer information.