To be fair, it's not that they're bad at it -- it's that they generally have an explicit philosophy against it. It's a choice.
Google management doesn't want to "pick winners". It prefers to let multiple products (like messaging apps, famously) compete and let the market decide. According to this way of thinking, you come out ahead in the long run because you increase your chances of having the winning product.
Gemini is a great example of when they do choose to focus on a single strategy, however. Cloud was another great example.