Parties in patent cases are often tempted to provide bare-bones responses to contention interrogatories, offering just enough to preserve their ability to expand on the arguments later during expert reports. That's easier, obviously, than providing more detailed contentions, and it also maintains flexibility as discovery develops.
Plus, parties simply may not have fully developed their theories at the time contention interrogatories are due. Expert reports are when theories are typically fully fleshed out, after discovery has closed and the universe of information is set, more or less.
But there is another consideration as well, beyond preventing a …