Answer
Why do publishers disagree about which countries qualify?
Because they use different classifications. Elsevier, Wiley, Sage and PLOS build on Research4Life. Taylor & Francis and Springer Nature use World Bank income bands with a GDP ceiling. IOP uses World Bank alone. ACM merges its EIFL and Research4Life agreements. Oxford combines three sources. The frameworks were built for different purposes and were never designed to agree.
Detail
Even the same basis produces different lists
Elsevier and Wiley both cite Research4Life. Elsevier's tiers cover 69 and 57 countries; Wiley's published lists cover 77 and 28. Each publisher adapts the framework to its own portfolio.