1. Its price!  The PowerBI Pro goes for only 10$ a month/user 2. Its simplicity for designing reports and dashboards 3. Its rich (and evolving all the time) community Add-ons 4. Its complete Software As A Service concept. Simple deployment.

It realy depends in your needs. It may serve as an E2E tool but, at some circumstnaces you will need to add - Data Warehouse, Paginated reporting tool, M/L tool, Data prep tool etc.