Why do so many researchers in CS fail to clarify their symbols and notations in research papers?
In the case of the first paper, the meaning of these equations are well-known within the subfield of reinforcement learning. (See Barto and Sutton's book for background.)

For instance, V is usually a value function which is the expected reward from following a policy π to termination. (The Q function - the value of taking an action from a state is also often used without full definition as well.)

I can't speak about CS as a whole, but in subfields like reinforcement learning, this is somewhat common. Personally, I find myself getting more and more formal the older I get. But, CS doesn't demand the same rigor as might be found in mathematics, so people get used to not providing it - and don't demand it of their graduate students.