I might not be the best person to answer this, but I'd like to know other people's thoughts as well in case I have something wrong. But from my understanding of things...
1. Yes. Power BI Premium still requires Power BI Pro Licenses. Premium gives you dedicated resources, # of front end cores and # of backend cores depending on which tier you purchase, along with some other added benfits. Pro licenses are still needed for sharing and collaboration. Viewers don't need Pro Licenses but editors who publish and share reports do. With Premium, you have the option to create both premium (using your dedicated capacity) or non-premium workspaces.
2. No.
3. Organization, structure, effeciency, cost, or management. Best guess is they probably don't want people creating a workspace for every report. By properly managing your worskspaces and permissions, you can better manage your reports and datasets. Long time excel users will sometimes like to create a new query and workbook for each use case on the same data instead of creating filters to use one report for multiple purposes which leads to... well, you know. So less outdated, unused information or "multiple versions of the truth" as well as reducing the number of datasets that are refreshing against your DBs for the same info and consuming resources.
