My theory is that, at the rate we develop technology, anything we throw at deep space is just going to get overtaken by something faster that we invent in the future, before it ever gets anywhere interesting. Which is why the premise of Star Trek: TMP, with Voyager returning to Earth was so silly. When the Enterprise went on her maiden voyage, she would have passed by wherever Voyager was puttering along at in a few minutes’ time.
Perhaps we will invent something that can travel faster than light. But even at the speed of light, it is four years travel time to the star closest to the Sun. Twice the speed of light, two years. Four times the speed of light, one year.
Practically speaking, why wait? The idea is that deep space may have rules that we don’t know about. If future tech does not pan out, we have still much to learn with slow and methodical.