Monetising usage and monetising data are two different things. Is IFTTT using my Day One data to make money ? - NO
Is it making money from my usage of Day one IFTTT integration - YES. It’s making money from the developer of Day One. Not me. This is a benefit Day One is providing its customers: Day One + IFTTT
I am using Day One as an example.
This is why it was important for me to understand their business model. Now my interpretation may be incorrect and I am happy to be corrected