activating a conda environment is not much more than applying settings to your shell to use a specific python interpreter (and the modules and libs associated to that interpreter)
when you drop out of a conda environment, your shell reverts to the python interpreter determined by your $PATH environment variable — generally speaking, this default is typically a non-conda environment and is usually the default python installed with the OS (if applicable)
As freude is saying, the obvious way to see this in action is to do which python as you activate/deactivate environments