Do you have a source for that?
The report to Council on the WEM Transit Centre building was expecting construction within 10-15 years, which in 2015 would have meant construction by 2030, and would have meant funding in place before that. Right now that timeline is right on.
"The current proposed alignment approved by Council incorporates an elevated LRT Station above the existing transit centre. The anticipated construction time frame is within 10-15 years, depending on the pace of future LRT expansion." CR_1978 April 22, 2015
By 2016, although I don't have a direct council report for this, the City said: "While there are no timelines for additional funding, the City hopes to be ready to initiate the procurement phase as early as 2018. Once additional funding is secured, it is planned to take about one year to select a contractor for the Valley Line West and another five years to complete construction."
Clearly the City figured they would be able to get funding a lot earlier than 2030.
edmonton.ca/projects_plans/transit/project-history
Besides, the refurb would have extended the life of the shelter building 10-15 years, sufficient to extend the life to 2030 so that still doesn't explain how they went back to doing a complete rebuild vs. the approved refurbishment.