Back in 1990, the RL didn't offer discounts or ticket deals as they do currently. I guess if you had the same offers back then, then I am sure the crowds would of been more at Wembley. Old Trafford and Elland Road were a sell out.
Also, the Aussies used to have massive travelling support (think Hull KR
, who came on orgainsed tours and were very much part of the atmosphere. Likewise when Britain toured down under ala the magic night in Melbourne. Magic moments like that, we are never likely to see again, and to me the game is much more poorer for it.