If by 'keeping libraries alive' you mean 'still using them' then millenials may be just like any other person who doesn't want to spend their own money for temp

If by 'keeping libraries alive' you mean 'still using them' then millenials may be just like any other person who doesn't want to spend their own money for temporary access to varied information sources. US Libraries in the 1970s, 80s and 90s were still logical places to do research and work. I don't believe they are anymore. They are mainly archives and public resources for those that can't afford information access privately. I remember very fondly visiting the library in the 70's and reading for hours there as a child but much prefer private access now.