The argument for Vancouver would be like this - IMO
1. Most of the facilities used previously that would be reused again would in 2030 need only minor upgrades - add another 12-30 years and we are talking major upgrades or new builds
2. Money has already been set aside for some of the community centres that could be used - they are likely to be built whether a bid happened or not, but a Games could allow for better facilities that might otherwise be built (hence public support?)
3. The big social issue in Vancouver is affordable housing/social housing - building a village for 30