Part of your assessment of every position is a look at what you attack and why the attacks can’t be turned into captures. In the current frame the only piece White attacks is Black’s bishop on d5. How is the bishop protected? By Black’s queen. The natural thought is to seek a safe and effective way to drive the queen from its perch. There is one move for White that satisfies those criteria: h3-h4. Of course Black would like to just move his queen to another square where it would be safe and still protect the d5 bishop. There is no such square, however; so once Black moves his queen to safety, White plays BxB. Lesson: don’t overlook pawns as tools for attacking the guards of pieces you want to take.