Pipedrive will only show the type that has data, if some kind of activity has no data it won’t appear, this will save space in the rendering, but can limit the informative power of the chart.
To get proper information out of it you have to know the data architecture behind it: how many different types of activity are available? Which are they? Why have they been created and what is the expected outcome of them? Only connecting the dots of missing information, will you really be able to figure out what is really going on in your team. The hiding of null data is common in chart development. It is done to make rendering clearer, but when you build data charts with rendering tools that create those shortcuts automatically, the building process will be easier, but users can be unaware of the complexity of data behind them.
Extract from Managing Sales Pipelines with Pipedrive CRM