Because they consolidated the belts, and because in WWE language they aren't "women," they're "divas," the Divas Title remained.
Same reason the World Tag Team Titles got abandoned after almost 30 years of lineage in favor of titles that still aren't even 10 years old yet. Consolidation to one set of titles, "WWE Tag Team Titles" got chosen over "World Tag Team Titles" for branding purposes.
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Thank you, Eddie Guerrero.
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