"It is my judgment, therefore, that we should not make it difficult for the Gentiles who are turning to God. Instead we should write to them, telling them to abstain from food polluted by idols, from sexual immorality, from the meat of strangled animals and from blood. For Moses has been preached in every city from the earliest times and is read in the synagogues on every Sabbath." (Acts 15:19-21)
This decision was for the Gentiles who are "turning to God". These are new converts, who are just starting to learn about God. So, instead of overwhelming them with too many things at first, they decided to just give them the things that are required for entry into the Synagogue. Forsake Idols, eat clean, and be sexually pure. These are the most important things for pagan Gentiles to learn first, because these things are so deeply associated with pagan worship practices.
People overlook Acts 15:21, but it is ver important:
"Moses has been preached in every city from the earliest times and is read in the synagogues on every Sabbath."
Why does this matter? Because these new Gentile converts were expected to attend Synagogue on the Sabbath and learn what Moses taught. You see, the apostles concluded that the Gentiles will learn Torah as they attend Synagogue every Sabbath.
It is obvious that there are more than four commandments that apply to Gentile converts. We obviously expect them to not murder, not steal, and not blaspheme. What about the two greatest commandments to love God and our Neighbor? Those obviously apply too, but they are not mentioned by the Jerusalem council. The only reason that these things are mentioned is because of their urgent application. These new Gentile converts (former pagans) were expected to immediately forsake and reject their paganism.
You see, even the early Gentile converts were expected to UNLEARN their pagan ways.