Innovation is a different skillset from maximizing profits of an existing product portfolio. Ballmer was pretty good at the latter and sucked at the former. With the exception of Azure (which was a little late to the party), the business lines that Ballmer milked were all initially developed under Gates.

The biggest years of profitability for most tech companies come after their innovation heyday (when they've already established their market position and no longer reinvest large amounts of cash into new product development), but without continued innovation a tech business eventually fades away into irrelevance.