They haven't been a member for some months. I would think the move to CAT 3C was a consequence rather than a cause. Aeros have recently announced a partnership with Tayside (see article
here) to create a "UK network of modular flight training schools". I think both ATOs resented the prominence of continental ATOs such as Bartolini and Diamond Flight Academy in the market, and thought that WA should be supporting UK schools only. We don't make that distinction, and take the view that each ATO has a different product in terms of quality, aircraft, price, customer service etc., and a good modular ATO should be able to stand in the market on its own merits, irrespective of location. Their competitor for CPL IR ME, Stapleford Flight Centre, is an enthusiastic member of the WA and seems to do perfectly well.