answer:Producers look at writing, market, contracts, and 1000 other variables, to determine when best to end a series. This was on Wikipedia “The show ended with its final 7th season 2-part episode “All Good Things…”, which brought the events of the series full circle, back to the original confrontation with Q. An interstellar anomaly that threatens all life in the universe forces Captain Picard to leap from his present, past and future to combat the threat. Picard was successfully able to demonstrate to Q that humanity could think outside of the confines of perception and theorize on new possibilities, while still being prepared to sacrifice themselves for the sake of the greater good. The show ended with the crew of the Enterprise feeling more like a family, and paved the way for four consecutive motion pictures that continued the theme and mission of the series.” I think the last sentence says it all.