Someone with second-edition rules might hesitate to buy The Traveller Book for several reasons:
Redundancy: If they already own the second edition rules, they might find much of the content overlapping, making the new purchase seem redundant. Additionally, some believe that Mongoose's second edition still inherits flaws from the first edition, adding little novelty for existing users (source).
Errors and Inconsistencies: There are often noted errors and inconsistencies in second-edition books. Some users report flaws in rule descriptions and examples which might deter current second-edition users from investing in what could be perceived as a similarly flawed book (source).
Scattered Rules: The Mongoose publications tend to spread rules across multiple books, complicating the experience for users who prefer consolidated rulesets. This could discourage a user from obtaining another book if it perpetuates this fragmented approach (source).
Investment in Existing Materials: Collectors and players often invest heavily in a particular edition. If someone already has a robust collection of second-edition materials, they might find it unnecessary and economically inefficient to switch or add another book that might not provide significant additional value.
If you have other specific concerns or aspects to consider, feel free to ask!