When I install multiple SQL Server instances on a same computer, every instance gets its own SQL Server Service for Analysis Services and Reporting Services. But I get only one service for Integration Service, why?
Integration Services is not "Instance aware". The rest (Analysis, Reporting, DB) are.
Note that SSIS doesn't need to be instance aware either. The service itself is pretty pointless and doesn't need to running. You simply need the SQL Server common binaries installed to run packages. The service is for SQL Server Agent and SSMS to browse packages etc