I think we would love to support more behavioral data recording, but that stuff is often difficult to define and observe and we want to make the observation process as simple as possible (and even with the way it currently works, it’s often not simple!). There’s always going to be a trade off between the amount of data you ask people to collect per observation and the number of total observations that are posted, and in general we err on the side of greater participation.
Currently, as others have said, there are workarounds like observation fields and projects, and it would be awesome to have a more robust system for recording behavior and interactions. For what it’s worth, here’s a feature request for adding interaction data: https://forum.inaturalist.org/t/add-interactions-to-species-pages/433 Wouldn’t be an easy lift, though.
Someone who’s pursued behavioral data via iNat is Greg Pauly at NHMLA. He asks people to post their observations of Elgaria mating holds and often follows up with them in real time. See this blog post.