Why?

There are multiples reasons to not use a pie/donut chart as it does not (most of the time) help to better understand the information presented. Edward Tufte and Stephen Few (both experts in data visualization) have given multiple arguments against pie charts. See the link for a good summary on the subject

https://priceonomics.com/should-you-ever-use-a-pie-chart/

My gripe with this edict is that it is not as relevant in the age of dashboards and interactive data. The same reason they were often a bad choice in static views, can be a positive within an interactive dashboard - a busy pie chart indicate visually that selection filters are not granular enough for the design criteria of the view.

You'd never use a pie chart? What if it's just more visually pleasing to the rest of your page design and you only want to convey roughly how say 3 data values compare in size?

They may be visually pleasing, but humans just cannot process angular magnitudes at a granular level.

A bar chart where one bar is 25% larger than another is obvious, a pie chart with the same is not obvious. Numeric labels are needed, because the chart itself does not serve as a useful visual reference.

It may look nice, but it does no good. Especially once you have more than a handful of values!

My point is making sometimes look good or to draw the eye of the user can be a big enough factor to use a pie chart. Maybe you're only showing two values and only need to convey if one value is larger or a lot larger than another for example.

Not every page is a scientific document.

If you are comparing 2 values, sure, maybe. But 40% versus 60% still won't be the most obvious thing other than "60% is larger", understanding the magnitude of the difference will involve more thinking, flat out. Taking more mental processing power to understand a visual chart is a bug, not a feature!

At this point you may as well write it longhand, "X is much larger than Y". Since promoting anything less than maximally accurate beliefs is an act of sabotage on your fellow human beings, you have to ask yourself why are you using a pie chart - because it's not to provide value for users.

That's a really extreme way to interpret what I said.

You can use a bar chart