I don't know if it's always worked this way, but for whatever reason the Mets started the 2020 season in OOTP with the international complex full. Apparently the AI will not/cannot sign players, and after a month or two in the season I got curious and started checking settings until I figured it out. If this happens just move a couple of the oldest kids up to the DSL and your scout can sign some new .5 star relief pitchers for you to cut in a couple of years